<!DOCTYPE article PUBLIC "-//FreeBSD//DTD DocBook V4.1-Based Extension//EN" [
<!ENTITY % man PUBLIC "-//FreeBSD//ENTITIES DocBook Manual Page Entities//EN">
%man;
<!ENTITY % authors PUBLIC "-//FreeBSD//ENTITIES DocBook Author Entities//EN">
%authors;
]>

<article>
  <articleinfo>
    <title>Storage Devices</title>
    
    <authorgroup>
      <author>
        <firstname>Wilko</firstname>
        <surname>Bulte</surname>
        
        <affiliation>
          <address><email>wilko@FreeBSD.org</email></address>
        </affiliation>
      </author>
    </authorgroup>
    
    <pubdate>$FreeBSD$</pubdate>
    
    <abstract>
      <para>This article talks about storage devices with FreeBSD.</para>
    </abstract>
  </articleinfo>
  
  <sect1 id="esdi">
    <title>Using ESDI hard disks</title>
      
    <para><emphasis>Copyright &copy; 1995, &a.wilko;.  24 September
      1995.</emphasis></para>
	  
    <para>ESDI is an acronym that means Enhanced Small Device
      Interface. It is loosely based on the good old ST506/412
      interface originally devised by Seagate Technology, the makers
      of the first affordable 5.25" winchester disk.</para>
	  
    <para>The acronym says Enhanced, and rightly so.  In the first
      place the speed of the interface is higher, 10 or 15
      Mbits/second instead of the 5 Mbits/second of ST412 interfaced
      drives.  Secondly some higher level commands are added, making
      the ESDI interface somewhat <quote>smarter</quote> to the operating system
      driver writers.  It is by no means as smart as SCSI by the way.
      ESDI is standardized by ANSI.</para>
	  
    <para>Capacities of the drives are boosted by putting more sectors
      on each track.  Typical is 35 sectors per track, high capacity
      drives I have seen were up to 54 sectors/track.</para>
      
    <para>Although ESDI has been largely obsoleted by IDE and SCSI
      interfaces, the availability of free or cheap surplus drives
      makes them ideal for low (or now) budget systems.</para>
      
      <sect2>
	<title>Concepts of ESDI</title>

	<sect3>
	  <title>Physical connections</title>
	  
	  <para>The ESDI interface uses two cables connected to each drive.
	    One cable is a 34 pin flat cable edge connector that carries the
	    command and status signals from the controller to the drive and
	    vice-versa.  The command cable is daisy chained between all the
	    drives.  So, it forms a bus onto which all drives are
	    connected.</para>
	      
	  <para>The second cable is a 20 pin flat cable edge connector that
	    carries the data to and from the drive.  This cable is radially
	    connected, so each drive has its own direct connection to the
	    controller.</para>
	      
	  <para>To the best of my knowledge PC ESDI controllers are limited to
	    using a maximum of 2 drives per controller.  This is compatibility
	    feature(?) left over from the WD1003 standard that reserves only a
	    single bit for device addressing.</para>
	</sect3>

	<sect3>
	  <title>Device addressing</title>
	  
	  <para>On each command cable a maximum of 7 devices and 1 controller
	    can be present.  To enable the controller to uniquely  identify
	    which drive it addresses, each ESDI device is equipped with
	    jumpers or switches to select the devices address.</para>
	      
	  <para>On PC type controllers the first drive is set to address 0,
	    the second disk to address 1.  <emphasis>Always make
	      sure</emphasis> you set each disk to an unique address! So, on a
	    PC with its two drives/controller maximum the first drive is drive
	    0, the second is drive 1.</para>
	</sect3>

	<sect3>
	  <title>Termination</title>
	  
	  <para>The daisy chained command cable (the 34 pin cable remember?)
	    needs to be terminated at the last drive on the chain.  For this
	    purpose ESDI drives come with a termination resistor network that
	    can be removed or disabled by a jumper when it is not used.</para>
	  
	  <para>So, one and <emphasis>only</emphasis> one drive, the one at
	    the farthest end of the command cable has its terminator
	    installed/enabled.  The controller automatically terminates the
	    other end of the cable.  Please note that this implies that the
	    controller must be  at one end of the cable and
	    <emphasis>not</emphasis> in the middle.</para>
	</sect3>
      </sect2>
      
      <sect2>
	<title>Using ESDI disks with FreeBSD</title>

	<para>Why is ESDI such a pain to get working in the first
	  place?</para>

	<para>People who tried ESDI disks with FreeBSD are known to have
	  developed a profound sense of frustration.  A combination of factors
	  works against you to produce effects that are hard to understand
	  when you have never seen them before.</para>
	    
	<para>This has also led to the popular legend ESDI and FreeBSD is a
	  plain NO-GO.  The following sections try to list all the pitfalls
	  and  solutions.</para>
	    
	<sect3>
	  <title>ESDI speed variants</title>
	  
	  <para>As briefly mentioned before, ESDI comes in two speed flavors.
	    The older drives and controllers use a 10 Mbits/second data
	    transfer rate.  Newer stuff uses 15 Mbits/second.</para>
	      
	  <para>It is not hard to imagine that 15 Mbits/second drive cause
	    problems on controllers laid out for 10 Mbits/second.  As always,
	    consult your controller <emphasis>and</emphasis> drive
	    documentation to see if things match.</para>
	</sect3>

	<sect3>
	  <title>Stay on track</title>
	  
	  <para>Mainstream ESDI drives use 34 to 36 sectors per track. Most
	    (older) controllers cannot handle more than this  number of
	    sectors.  Newer, higher capacity, drives use higher numbers of
	    sectors per track.  For instance, I own a 670 MB drive that has 54
	    sectors per track.</para>
	      
	  <para>In my case, the controller could not handle this number of
	    sectors.  It proved to work well except that it only used 35
	    sectors on each track.  This meant losing a lot of disk
	    space.</para>
	      
	  <para>Once again, check the documentation of your hardware for more
	    info.  Going out-of-spec like in the example might or might not
	    work.  Give it a try or get another more capable
	    controller.</para>
	</sect3>

	<sect3>
	  <title>Hard or soft sectoring</title>
	  
	  <para>Most ESDI drives allow hard or soft sectoring to be selected
	    using a jumper.  Hard sectoring means that the drive will produce
	    a sector pulse on the start of each new sector. The controller
	    uses this pulse to tell when it should start to write or
	    read.</para>
	  
	  <para>Hard sectoring allows a selection of sector size (normally
	    256, 512 or 1024 bytes per formatted sector).  FreeBSD uses 512
	    byte sectors.  The number of sectors per track also varies while
	    still using the same number of bytes per formatted sector.  The
	    number of <emphasis>unformatted</emphasis> bytes per sector
	    varies, dependent on your controller it needs more or less
	    overhead  bytes to work correctly.  Pushing more sectors on a
	    track  of course gives you more usable space, but might give
	    problems if your controller needs more bytes than the  drive
	    offers.</para>
	      
	  <para>In case of soft sectoring, the controller itself determines
	    where to start/stop reading or writing.  For ESDI hard sectoring
	    is the default (at least on everything I came across).  I never
	    felt the urge to try soft sectoring.</para>
	      
	  <para>In general, experiment with sector settings before you install
	    FreeBSD because you need to re-run the low-level format after each
	    change.</para>
	</sect3>

	<sect3>
	  <title>Low level formatting</title>
	  
	  <para>ESDI drives need to be low level formatted before they are
	    usable.  A reformat is needed whenever you figgle with the number
	    of sectors/track jumpers or the physical orientation of the drive
	    (horizontal, vertical).  So, first think, then format.  The format
	    time must not be underestimated, for big disks it can take
	    hours.</para>
	      
	  <para>After a low level format, a surface scan is done to find and
	    flag bad sectors.  Most disks have a manufacturer bad block list
	    listed on a piece of paper or adhesive sticker.  In addition, on
	    most disks the list is also written onto the disk.  Please use the
	    manufacturer's list.  It is much easier to remap a defect now than
	    after FreeBSD is installed.</para>
	      
	  <para>Stay away from low-level formatters that mark all sectors of a
	    track as bad as soon as they find one bad sector.  Not only does
	    this waste space, it also and more importantly causes you grief
	    with bad144 (see the section on bad144).</para>
	</sect3>

	<sect3>
	  <title>Translations</title>
	  
	  <para>Translations, although not exclusively a ESDI-only problem,
	    might give you real trouble.  Translations come in multiple
	    flavors.  Most of them  have in common that they attempt to work
	    around the limitations posed upon disk geometries by the original
	    IBM PC/AT design (thanks IBM!).</para>
	      
	  <para>First of all there is the (in)famous 1024 cylinder limit. For
	    a system to be able to boot, the stuff (whatever operating system)
	    must be in the first 1024 cylinders of a disk.  Only 10 bits are
	    available to encode the cylinder number.  For the number of
	    sectors the limit is 64 (0-63).  When you combine the 1024
	    cylinder limit with the 16 head limit (also a design feature) you
	    max out at fairly limited  disk sizes.</para>
	      
	  <para>To work around this problem, the manufacturers of ESDI PC
	    controllers added a BIOS prom extension on their boards.  This
	    BIOS extension handles disk I/O for booting (and for some
	    operating systems <emphasis>all</emphasis> disk I/O) by using
	    translation.  For instance, a big drive might be presented to the
	    system as having 32 heads and 64 sectors/track.  The result is
	    that the number of cylinders is reduced to something below 1024
	    and is therefore usable by the system without problems.  It is
	    noteworthy to know that FreeBSD does not use the BIOS after its
	    kernel has started.  More on this later.</para>
	      
	  <para>A second reason for translations is the fact that most older
	    system BIOSes could only handle drives with 17 sectors per track
	    (the old ST412 standard).  Newer system BIOSes usually have a
	    user-defined drive type (in most cases this is drive type
	    47).</para>

	  <warning>
	    <para>Whatever you do to translations after reading this document,
	      keep in mind that if you have multiple operating systems on the
	      same disk, all must use the same translation</para>
	  </warning>
	  
	  <para>While on the subject of translations, I have seen one
	    controller type (but there are probably more like this) offer the
	    option to logically split a drive in multiple partitions as a BIOS
	    option.  I had select 1 drive == 1 partition because this
	    controller wrote this info onto the disk.  On power-up it read the
	    info and presented itself to the system based on the info from the
	    disk.</para>
	</sect3>
	    
	<sect3>
	  <title>Spare sectoring</title>
	  
	  <para>Most ESDI controllers offer the possibility to remap bad
	    sectors.  During/after the low-level format of the disk bad
	    sectors are marked as such, and a replacement sector is put in
	    place (logically of course) of the bad one.</para>
	      
	  <para>In most cases the remapping is done by using N-1 sectors on
	    each track for actual data storage, and sector N itself is the
	    spare sector.  N is the total number of sectors physically
	    available on the track.  The idea behind this is that the
	    operating system sees a <quote>perfect</quote> disk without bad sectors.  In
	    the case of FreeBSD this concept is not usable.</para>
	      
	  <para>The problem is that the translation from
	    <emphasis>bad</emphasis> to <emphasis>good</emphasis> is performed
	    by the BIOS of the ESDI controller.  FreeBSD, being a true 32 bit
	    operating system, does not use the BIOS after it has been booted.
	    Instead, it has device drivers that talk directly to the
	    hardware.</para>
	      
	  <para><emphasis>So: do not use spare sectoring, bad block remapping
	      or whatever it may be called by the controller manufacturer when
	      you want to use the disk for FreeBSD.</emphasis></para>
	</sect3>

	<sect3>
	  <title>Bad block handling</title>
	  
	  <para>The preceding section leaves us with a problem.  The
	    controller's bad block handling is not usable and still FreeBSD's
	    filesystems assume perfect media without any flaws. To solve this
	    problem, FreeBSD use the <command>bad144</command> tool.  Bad144
	    (named after a Digital Equipment standard for bad block handling)
	    scans a FreeBSD slice for bad blocks.  Having found these bad
	    blocks, it writes a table with the offending block numbers to the
	    end of the FreeBSD slice.</para>
	      
	  <para>When the disk is in operation, the disk accesses are checked
	    against the table read from the disk.  Whenever a block number is
	    requested that is in the <command>bad144</command> list, a
	    replacement block (also from the end of the FreeBSD slice) is
	    used.  In this way, the <command>bad144</command> replacement
	    scheme presents <quote>perfect</quote> media to the FreeBSD filesystems.</para>
	      
	  <para>There are a number of potential pitfalls associated with the
	    use of <command>bad144</command>.  First of all, the slice cannot
	    have more than 126 bad sectors.  If your drive has a high number
	    of bad sectors, you might need to divide it into multiple FreeBSD
	    slices each containing less than 126 bad sectors.  Stay away from
	    low-level format programs that mark <emphasis>every</emphasis>
	    sector of a track as bad when  they find a flaw on the track.  As
	    you can imagine, the  126 limit is quickly reached when the
	    low-level format is done this way.</para>
	      
	  <para>Second, if the slice contains the root filesystem, the slice
	    should be within the 1024 cylinder BIOS limit.  During the boot
	    process the bad144 list is read using the BIOS and this only
	    succeeds when the list is within the 1024 cylinder limit.</para>

	  <note>
	    <para>The restriction is not that only the root
	      <emphasis>filesystem</emphasis> must be within the 1024 cylinder
	      limit, but rather the entire <emphasis>slice</emphasis> that
	      contains the root filesystem.</para>
	  </note>
	</sect3>

	<sect3>
	  <title>Kernel configuration</title>
	  
	  <para>ESDI disks are handled by the same <literal>wd</literal>driver
	    as IDE and ST412 MFM disks.  The <literal>wd</literal> driver
	    should work for all WD1003 compatible interfaces.</para>
	      
	  <para>Most hardware is jumperable for one of two different I/O
	    address ranges and IRQ lines.  This allows you to have  two wd
	    type controllers in one system.</para>
	  
	  <para>When your hardware allows non-standard strappings, you can use
	    these with FreeBSD as long as you enter the  correct info into the
	    kernel config file.  An example from the kernel config file (they
	    live in <filename>/sys/i386/conf</filename> BTW).</para>
	      
	  <programlisting># First WD compatible controller
controller      wdc0    at isa? port "IO_WD1" bio irq 14 vector wdintr
disk            wd0     at wdc0 drive 0
disk            wd1     at wdc0 drive 1
# Second WD compatible controller
controller      wdc1    at isa? port "IO_WD2" bio irq 15 vector wdintr
disk            wd2     at wdc1 drive 0
disk            wd3     at wdc1 drive 1</programlisting>
	</sect3>
      </sect2>
      
      <sect2>
	<title>Particulars on ESDI hardware</title>

	<sect3>
	  <title>Adaptec 2320 controllers</title>
	  
	  <para>I successfully installed FreeBSD onto a ESDI disk controlled
	    by a ACB-2320.  No other operating system was present on the
	    disk.</para>
	      
	  <para>To do so I low level formatted the disk using
	    <command>NEFMT.EXE</command> (<command>ftp</command>able from
	    <hostid role="fqdn">www.adaptec.com</hostid>) and answered NO to
	    the question whether the disk should be formatted with a spare
	    sector on each track.  The BIOS on the ACD-2320 was disabled.  I
	    used the <literal>free configurable</literal> option in the system
	    BIOS to allow the BIOS to boot it.</para>
	      
	  <para>Before using <command>NEFMT.EXE</command> I tried to format
	    the disk using the ACB-2320 BIOS built-in formatter.  This proved
	    to be a show stopper, because it did not give me an option to
	    disable spare sectoring.  With spare sectoring enabled the FreeBSD
	    installation process broke down on the <command>bad144</command>
	    run.</para>
	      
	  <para>Please check carefully which
	    ACB-232<replaceable>xy</replaceable> variant you have. The
	    <replaceable>x</replaceable> is either <literal>0</literal> or
	    <literal>2</literal>, indicating a controller without or with a
	    floppy controller on board.</para>
	      
	  <para>The <literal>y</literal> is more interesting.  It can either
	    be a blank, a <literal>A-8</literal> or a <literal>D</literal>.  A
	    blank indicates a plain 10 Mbits/second controller.  An
	    <literal>A-8</literal> indicates a 15 Mbits/second controller
	    capable of handling 52 sectors/track.  A <literal>D</literal>
	    means a 15 Mbits/second controller that can also handle drives
	    with &gt; 36 sectors/track (also 52?).</para>
	      
	  <para>All variations should be capable of using 1:1 interleaving.
	    Use 1:1, FreeBSD is fast enough to handle it.</para>
	</sect3>

	<sect3>
	  <title>Western Digital WD1007 controllers</title>
	  
	  <para>I successfully installed FreeBSD onto a ESDI disk controlled
	    by a WD1007 controller.  To be precise, it was a WD1007-WA2.
	    Other variations of the WD1007 do exist.</para>
	      
	  <para>To get it to work, I had to disable the sector translation and
	    the WD1007's onboard BIOS.  This implied I could not use the
	    low-level formatter built into this BIOS.  Instead, I grabbed
	    <command>WDFMT.EXE</command> from <hostid
	      role="fqdn">www.wdc.com</hostid> Running this formatted my drive
	    just fine.</para>
	</sect3>

	<sect3>
	  <title>Ultrastor U14F controllers</title>
	  
	  <para>According to multiple reports from the net, Ultrastor ESDI
	    boards work OK with FreeBSD.  I lack any further info on
	    particular settings.</para>
	</sect3>
      </sect2>
      
      <sect2 id="esdi-further-reading">
	<title>Further reading</title>
	    
	<para>If you intend to do some serious ESDI hacking, you might want to
	  have the official standard at hand:</para>
	    
	<para>The latest ANSI X3T10 committee document is: Enhanced Small
	  Device Interface (ESDI) [X3.170-1990/X3.170a-1991]    [X3T10/792D
	  Rev 11]</para>
		
	<para>On Usenet the newsgroup <ulink
	    url="news:comp.periphs">comp.periphs</ulink> is a noteworthy place
	  to look  for more info.</para>
	    
	<para>The World Wide Web (WWW) also proves to be a very handy info
	  source: For info on Adaptec ESDI controllers see <ulink
	    url="http://www.adaptec.com/">http://www.adaptec.com/</ulink>. For
	  info on Western Digital controllers see <ulink
	    url="http://www.wdc.com/">http://www.wdc.com/</ulink>.</para>
      </sect2>
      
      <sect2>
	<title>Thanks to...</title>

	<para>Andrew Gordon for sending me an Adaptec 2320 controller and ESDI
	  disk for testing.</para>
      </sect2>
    </sect1>
    
    <sect1 id="scsi">
      <title>What is SCSI?</title>
      
      <para><emphasis>Copyright &copy; 1995, &a.wilko;.  July 6,
	  1996.</emphasis></para>
	  
      <para>SCSI is an acronym for Small Computer Systems Interface.  It is an
	ANSI standard that has become one of the leading I/O buses in the
	computer industry.  The foundation of the SCSI standard was laid by
	Shugart Associates (the same guys that gave the world the first mini
	floppy disks) when they introduced the SASI bus (Shugart Associates
	Standard Interface).</para>
	  
      <para>After some time an industry effort was started to come to a more
	strict standard allowing devices from different vendors to work
	together.  This effort was recognized in the ANSI SCSI-1 standard.
	The SCSI-1 standard (approximately 1985) is rapidly becoming obsolete.  The
	current standard is SCSI-2 (see <link
	  linkend="scsi-further-reading">Further reading</link>), with SCSI-3
	on the drawing boards.</para>
	  
      <para>In addition to a physical interconnection standard, SCSI defines a
	logical (command set) standard to which disk devices must adhere.
	This standard is called the Common Command Set (CCS) and was developed
	more or less in parallel with ANSI SCSI-1. SCSI-2 includes the
	(revised) CCS as part of the standard itself. The commands are
	dependent on the type of device at hand.  It does not make much sense
	of course to define a Write command for a scanner.</para>
	  
      <para>The SCSI bus is a parallel bus, which comes in a number of
	variants.  The oldest and most used is an 8 bit wide bus, with
	single-ended signals, carried on 50 wires.  (If you do not know what
	single-ended means, do not worry, that is what this document is all
	about.)  Modern designs also use 16 bit wide buses, with differential
	signals.  This allows transfer speeds of 20Mbytes/second, on cables
	lengths of up to 25 meters.  SCSI-2 allows a maximum bus width of 32
	bits, using an additional cable. Quickly emerging are Ultra SCSI (also
	called Fast-20) and Ultra2 (also called Fast-40).  Fast-20 is 20
	million transfers per second (20 Mbytes/sec on a 8 bit bus), Fast-40
	is 40 million transfers per second (40 Mbytes/sec on a 8 bit bus).
	Most hard drives sold today are single-ended Ultra SCSI (8 or 16
	bits).</para>
	  
      <para>Of course the SCSI bus not only has data lines, but also a number
	of control signals.  A very elaborate protocol is part of the standard
	to allow multiple devices to share the bus in an efficient manner.  In
	SCSI-2, the data is always checked using a separate parity line.  In
	pre-SCSI-2 designs parity was optional.</para>
	  
      <para>In SCSI-3 even faster bus types are introduced, along with a
	serial SCSI busses that reduces the cabling overhead and allows a
	higher maximum bus length.  You might see names like SSA and
	fibre channel in this context.  None of the serial buses are currently
	in widespread use (especially not in the typical FreeBSD environment).
	For this reason the serial bus types are not discussed any
	further.</para>
	  
      <para>As you could have guessed from the description above, SCSI devices
	are intelligent.  They have to be to adhere to the SCSI standard
	(which is over 2 inches thick BTW).  So, for a hard disk drive for
	instance you do not specify a head/cylinder/sector to address a
	particular block, but simply the number of the block you want.
	Elaborate caching schemes, automatic bad block replacement etc are all
	made possible by this <quote>intelligent device</quote> approach.</para>
	  
      <para>On a SCSI bus, each possible pair of devices can communicate.
	Whether their function allows this is another matter, but the standard
	does not restrict it.  To avoid signal contention, the 2 devices have
	to arbitrate for the bus before using it.</para>
	  
      <para>The philosophy of SCSI is to have a standard that allows
	older-standard devices to work with newer-standard ones.  So, an old
	SCSI-1 device should normally work on a SCSI-2 bus.  I say Normally,
	because it is not absolutely sure that the implementation of an old
	device follows the (old) standard closely enough to be acceptable on a
	new bus.  Modern devices are usually more well-behaved, because the
	standardization has become more strict and is better adhered to by the
	device manufacturers.</para>
	  
      <para>Generally speaking, the chances of getting a working set of
	devices on a single bus is better when all the devices are SCSI-2 or
	newer.  This implies that you do not have to dump all your old stuff
	when you get that shiny 2GB disk: I own a system on which a pre-SCSI-1
	disk, a SCSI-2 QIC tape unit, a SCSI-1 helical scan tape unit and 2
	SCSI-1 disks work together quite happily.  From a performance
	standpoint you might want to separate your older and newer (=faster)
	devices however.</para>
      
      <sect2>
	<title>Components of SCSI</title>

	<para>As said before, SCSI devices are smart.  The idea is to put the
	  knowledge about intimate hardware details onto the SCSI device
	  itself.  In this way, the host system does not have to worry about
	  things like how many heads a hard disks has, or how many tracks
	  there are on a specific tape device.  If you are curious, the
	  standard specifies commands with which you can query your devices on
	  their hardware particulars.  FreeBSD uses this capability during
	  boot to check out what devices are connected and whether they need
	  any special treatment.</para>
	    
	<para>The advantage of intelligent devices is obvious: the device
	  drivers on the host can be made in a much more generic fashion,
	  there is no longer a need to change (and qualify!) drivers for every
	  odd new device that is introduced.</para>
	    
	<para>For cabling and connectors there is a golden rule: get good
	  stuff.  With bus speeds going up all the time you will save yourself
	  a lot of grief by using good material.</para>
	    
	<para>So, gold plated connectors, shielded cabling, sturdy connector
	  hoods with strain reliefs etc are the way to go. Second golden rule:
	  do no use cables longer than necessary.  I once spent 3 days hunting
	  down a problem with a flaky machine only to discover that shortening
	  the SCSI bus by 1 meter solved the problem.  And the original bus
	  length was well within the SCSI specification.</para>
      </sect2>
	  
      <sect2>
	<title>SCSI bus types</title>

	<para>From an electrical point of view, there are two incompatible bus
	  types: single-ended and differential.  This means that there are two
	  different main groups of SCSI devices and controllers, which cannot
	  be mixed on the same bus.  It is possible however to use special
	  converter hardware to transform a single-ended bus into a
	  differential one (and vice versa).  The differences between the bus
	  types are explained in the next sections.</para>
	    
	<para>In lots of SCSI related documentation there is a sort of jargon
	  in use to abbreviate the different bus types.  A small list:</para>
	    
	<itemizedlist>
	  <listitem>
	    <para>FWD:	Fast Wide Differential</para>
	  </listitem>
	  
	  <listitem>
	    <para>FND:	Fast Narrow Differential</para>
	  </listitem>
	  
	  <listitem>
	    <para>SE:	Single Ended</para>
	  </listitem>
	  
	  <listitem>
	    <para>FN:	Fast Narrow</para>
	  </listitem>
	  
	  <listitem>
	    <para>etc.</para>
	  </listitem>
	</itemizedlist>


	<para>With a minor amount of imagination one can usually imagine what
	  is meant.</para>
	    
	<para>Wide is a bit ambiguous, it can indicate 16 or 32 bit buses. As
	  far as I know, the 32 bit variant is not (yet) in use, so wide
	  normally means 16 bit.</para>
	    
	<para>Fast means that the timing on the bus is somewhat different, so
	  that on a narrow (8 bit) bus 10 Mbytes/sec are possible instead of 5
	  Mbytes/sec for <quote>slow</quote> SCSI.  As discussed before, bus speeds of 20
	  and 40 million transfers/second are also emerging  (Fast-20 == Ultra
	  SCSI and Fast-40 == Ultra2 SCSI).</para>

	<note>
	  <para>The data lines &gt; 8 are only used for data transfers and
	    device addressing.  The transfers of commands and status messages
	    etc are only performed on the lowest 8 data lines. The standard
	    allows narrow devices to operate on a wide bus. The usable bus
	    width is negotiated between the devices.  You have to watch your
	    device addressing closely when mixing wide and narrow.</para>
	</note>

	<sect3>
	  <title>Single ended buses</title>
	  
	  <para>A single-ended SCSI bus uses signals that are either 5 Volts
	    or 0 Volts (indeed, TTL levels) and are relative to a COMMON
	    ground reference.  A singled ended 8 bit SCSI bus has
	    approximately 25 ground lines, who are all tied to a single <quote>rail</quote>
	    on all devices.  A standard single ended bus has a maximum length
	    of 6 meters.  If the same bus is used with fast-SCSI devices, the
	    maximum length allowed drops to 3 meters.  Fast-SCSI means that
	    instead of 5Mbytes/sec the bus allows 10Mbytes/sec
	    transfers.</para>
	      
	  <para>Fast-20 (Ultra SCSI) and Fast-40 allow for 20 and 40 million
	    transfers/second respectively.  So, F20 is 20 Mbytes/second on a 8
	    bit bus, 40 Mbytes/second on a 16 bit bus etc.  For F20 the max
	    bus length is 1.5 meters, for F40 it becomes 0.75 meters.  Be
	    aware that F20 is pushing  the limits quite a bit, so you will
	    quickly find out if your SCSI bus is electrically sound.</para>

	  <note>
	    <para>If some devices on your bus use <quote>fast</quote> to communicate your
	      bus must adhere to the length restrictions for fast
	      buses!</para>
	  </note>
	  
	  <para>It is obvious that with the newer fast-SCSI devices the bus
	    length can become a real bottleneck.  This is why the differential
	    SCSI bus was introduced in the SCSI-2 standard.</para>
	      
	  <para>For connector pinning and connector types please refer to the
	    SCSI-2 standard (see <link linkend="scsi-further-reading">Further
	      reading</link>) itself, connectors etc are listed there in
	    painstaking detail.</para>
	  
	  <para>Beware of devices using non-standard cabling.  For instance
	    Apple uses a 25pin D-type connecter (like the one on serial ports
	    and parallel printers).  Considering that the official SCSI bus
	    needs 50 pins you can imagine the use of this connector needs some
	    <quote>creative cabling</quote>.  The reduction of the number of ground wires
	    they used is a bad idea, you better stick to 50 pins cabling  in
	    accordance with the SCSI standard.  For Fast-20 and 40 do not even
	    think about buses like this.</para>
	</sect3>

	<sect3>
	  <title>Differential buses</title>
	  
	  <para>A differential SCSI bus has a maximum length of 25 meters.
	    Quite a difference from the 3 meters for a single-ended fast-SCSI
	    bus.  The idea behind differential signals is that each bus signal
	    has its own return wire.  So, each signal is carried on a
	    (preferably twisted) pair of wires.  The voltage difference
	    between these two wires determines whether the signal is asserted
	    or de-asserted.  To a certain extent the voltage difference
	    between ground and the signal wire pair is not relevant (do not
	    try 10 kVolts though).</para>
	      
	  <para>It is beyond the scope of this document to explain why this
	    differential idea is so much better.  Just accept that
	    electrically seen the use of differential signals gives a much
	    better noise margin.  You will normally find differential buses in
	    use for inter-cabinet connections.  Because of the lower cost
	    single ended is mostly used for shorter buses like inside
	    cabinets.</para>
	      
	  <para>There is nothing that stops you from using differential stuff
	    with FreeBSD, as long as you use a controller that has device
	    driver support in FreeBSD.  As an example, Adaptec marketed the
	    AHA1740 as a single ended board, whereas the AHA1744 was
	    differential.  The software interface to the host is identical for
	    both.</para>
	</sect3>

	<sect3>
	  <title>Terminators</title>
	  
	  <para>Terminators in SCSI terminology are resistor networks that are
	    used to get a correct impedance matching.  Impedance matching is
	    important to get clean signals on the bus, without reflections or
	    ringing.  If you once made a long distance telephone call on a bad
	    line you probably know what reflections are.  With 20Mbytes/sec
	    traveling over your SCSI bus, you do not want signals echoing
	    back.</para>
	      
	  <para>Terminators come in various incarnations, with more or less
	    sophisticated designs.  Of course, there are internal and external
	    variants.  Many SCSI devices come with a number of sockets in
	    which a number of resistor networks can (must be!) installed.  If
	    you remove terminators from a device, carefully store them.  You
	    will need them when you ever decide to reconfigure your SCSI bus.
	    There is enough variation in even these simple tiny things to make
	    finding the exact replacement a frustrating business.  There are
	    also SCSI devices that have a single jumper to enable or disable a
	    built-in terminator. There are special terminators you can stick
	    onto a flat cable bus.  Others look like external connectors, or a
	    connector hood without a cable.  So, lots of choice as you can
	    see.</para>
	      
	  <para>There is much debate going on if and when you should switch
	    from simple resistor (passive) terminators to active terminators.
	    Active terminators contain slightly more elaborate circuit to give
	    cleaner bus signals.  The general consensus seems to be that the
	    usefulness of active termination increases when you have long
	    buses and/or fast devices.  If you ever have problems with your
	    SCSI buses you might consider trying an active terminator.  Try to
	    borrow one first, they reputedly are quite expensive.</para>
	      
	  <para>Please keep in mind that terminators for differential and
	    single-ended buses are not identical.  You should <emphasis>not
	      mix</emphasis> the two variants.</para>
	      
	  <para>OK, and now where should you install your terminators? This is
	    by far the most misunderstood part of SCSI.  And it is by far the
	    simplest.  The rule is: <emphasis>every single line on the SCSI
	      bus has 2 (two) terminators, one at each end of the
	      bus.</emphasis> So, two and not one or three or whatever.  Do
	    yourself a favor and stick to this rule.  It will save you endless
	    grief, because wrong termination has the potential to introduce
	    highly mysterious bugs.  (Note the <quote>potential</quote> here;
	    the nastiest part is that it may or may not work.)</para>
	      
	  <para>A common pitfall is to have an internal (flat) cable in a
	    machine and also an external cable attached to the controller. It
	    seems almost everybody forgets to remove the terminators from the
	    controller.  The terminator must now be on the last external
	    device, and not on the controller! In general, every
	    reconfiguration of a SCSI bus must pay attention to this.</para>

	  <note>
	    <para>Termination is to be done on a per-line basis.  This means
	      if you have both narrow and wide buses connected to the same
	      host adapter, you need to enable termination on the higher 8
	      bits of the bus on the adapter (as well as the last devices on
	      each bus, of course).</para>
	      </note>
	      
	  <para>What I did myself is remove all terminators from my SCSI
	    devices and controllers.  I own a couple of external terminators,
	    for both the Centronics-type external cabling and for the internal
	    flat cable connectors.  This makes reconfiguration much
	    easier.</para>
	      
	  <para>On modern devices, sometimes integrated terminators are used.
	    These things are special purpose integrated circuits that can be
	    enabled or disabled with a control pin.  It is not necessary to
	    physically remove them from a device.  You may find them on newer
	    host adapters, sometimes they are software configurable, using
	    some sort of setup tool.  Some will even auto-detect the cables
	    attached to the connectors and automatically set up the
	    termination as necessary.  At any rate, consult your
	    documentation!</para>
	</sect3>

	<sect3>
	  <title>Terminator power</title>
	  
	  <para>The terminators discussed in the previous chapter need power
	    to operate properly.  On the SCSI bus, a line is dedicated to this
	    purpose.  So, simple huh?</para>
	      
	  <para>Not so.  Each device can provide its own terminator power to
	    the terminator sockets it has on-device.  But if you have external
	    terminators, or when the device supplying the terminator power to
	    the SCSI bus line is switched off you are in trouble.</para>
	      
	  <para>The idea is that initiators (these are devices that initiate
	    actions on the bus, a discussion follows) must supply terminator
	    power.  All SCSI devices are allowed (but not required) to supply
	    terminator power.</para>
	      
	  <para>To allow for un-powered devices on a bus, the terminator power
	    must be supplied to the bus via a diode.  This prevents the
	    backflow of current to un-powered devices.</para>
	      
	  <para>To prevent all kinds of nastiness, the terminator power is
	    usually fused.  As you can imagine, fuses might blow.  This can,
	    but does not have to, lead to a non functional bus.  If multiple
	    devices supply terminator power, a single blown fuse will not put
	    you out of business.  A single supplier with a blown fuse
	    certainly will.  Clever external terminators sometimes have a  LED
	    indication that shows whether terminator power is present.</para>
	      
	  <para>In newer designs auto-restoring fuses that <quote>reset</quote> themselves
	    after some time are sometimes used.</para>
	</sect3>

	<sect3>
	  <title>Device addressing</title>
	  
	  <para>Because the SCSI bus is, ehh, a bus there must be a way to
	    distinguish or address the different devices connected to
	    it.</para>
	      
	  <para>This is done by means of the SCSI or target ID.  Each device
	    has a unique target ID.  You can select the ID to which a device
	    must respond using a set of jumpers, or a dip switch, or something
	    similar.  Some SCSI host adapters let you change the target ID
	    from the boot menu.  (Yet some others will not let you change the
	    ID from 7.)  Consult the documentation of your device for more
	    information.</para>
	  
	  <para>Beware of multiple devices configured to use the same ID.
	    Chaos normally reigns in this case.  A pitfall is that one of the
	    devices sharing the same ID sometimes even manages to answer to
	    I/O requests!</para>
	      
	  <para>For an 8 bit bus, a maximum of 8 targets is possible.  The
	    maximum is 8 because the selection is done bitwise using the 8
	    data lines on the bus.  For wide buses this increases to the
	    number of data lines (usually 16).</para>

	  <note>
	    <para>A narrow SCSI device can not communicate with a SCSI device
	      with a target ID larger than 7.  This means it is generally not
	      a good idea to move your SCSI host adapter's target ID to
	      something higher than 7 (or your CDROM will stop
	      working).</para>
	  </note>
	  
	  <para>The higher the SCSI target ID, the higher the priority the
	    devices has.  When it comes to arbitration between devices that
	    want to use the bus at the same time, the device that has the
	    highest SCSI ID will win.  This also means that the SCSI host
	    adapter usually uses target ID 7.  Note however that the lower 8
	    IDs have higher priorities than the higher 8 IDs on a wide-SCSI
	    bus.  Thus, the order of target IDs is: [7 6 .. 1 0 15 14 .. 9 8]
	    on a wide-SCSI system.  (If you are wondering why the lower 8
	    have higher priority, read the previous paragraph for a
	    hint.)</para>
	      
	  <para>For a further subdivision, the standard allows for Logical
	    Units or LUNs for short.  A single target ID may have multiple
	    LUNs.  For example, a tape device including a tape changer may
	    have LUN 0 for the tape device itself, and LUN 1 for the tape
	    changer.  In this way, the host system can address each of the
	    functional units of the tape changer as desired.</para>
	</sect3>
	    
	<sect3>
	  <title>Bus layout</title>
	  
	  <para>SCSI buses are linear.  So, not shaped like Y-junctions, star
	    topologies, rings, cobwebs or whatever else people might want to
	    invent.  One of the most common mistakes is for people with
	    wide-SCSI host adapters to connect devices on all three connecters
	    (external connector, internal wide connector, internal narrow
	    connector).  Do not do that.  It may appear to work if you are
	    really lucky, but I can almost guarantee that your system will
	    stop functioning at the most unfortunate moment (this is also
	    known as <quote>Murphy's law</quote>).</para>
	      
	  <para>You might notice that the terminator issue discussed earlier
	    becomes rather hairy if your bus is not linear.  Also, if you have
	    more connectors than devices on your internal SCSI cable, make
	    sure you attach devices on connectors on both ends instead of
	    using the connectors in the middle and let one or both ends
	    dangle.  This will screw up the termination of the bus.</para>
	      
	  <para>The electrical characteristics, its noise margins and
	    ultimately the reliability of it all are tightly related to linear
	    bus rule.</para>
	  
	  <para><emphasis>Stick to the linear bus rule!</emphasis></para>
	</sect3>
      </sect2>
      
      <sect2>
	<title>Using SCSI with FreeBSD</title>

	<sect3>
	  <title>About translations, BIOSes and magic...</title>
	  
	  <para>As stated before, you should first make sure that you have a
	    electrically sound bus.</para>
	      
	  <para>When you want to use a SCSI disk on your PC as boot disk, you
	    must aware of some quirks related to PC BIOSes.  The PC BIOS in
	    its first incarnation used a low level physical interface to the
	    hard disk.  So, you had to tell the BIOS (using a setup tool or a
	    BIOS built-in setup) how your disk physically looked like.  This
	    involved stating number of heads, number of cylinders, number of
	    sectors per track, obscure things like precompensation and reduced
	    write current cylinder etc.</para>
	      
	  <para>One might be inclined to think that since SCSI disks are smart
	    you can forget about this.  Alas, the arcane setup issue is still
	    present today.  The system BIOS needs to know how to access your
	    SCSI disk with the head/cyl/sector method in order to load the
	    FreeBSD kernel during boot.</para>
	      
	  <para>The SCSI host adapter or SCSI controller you have put in your
	    AT/EISA/PCI/whatever bus to connect your disk therefore has its
	    own on-board BIOS.  During system startup, the SCSI BIOS takes
	    over the hard disk interface routines from the system BIOS.  To
	    fool the system BIOS, the system setup is normally set to No hard
	    disk present.  Obvious, is it not?</para>
	      
	  <para>The SCSI BIOS itself presents to the system a so called
	    <emphasis>translated</emphasis> drive.  This means that a fake
	    drive table is constructed that allows the PC to boot the drive.
	    This translation is often (but not always) done using a pseudo
	    drive with 64 heads and 32 sectors per track.  By varying the
	    number of cylinders, the SCSI BIOS adapts to the actual drive
	    size.  It is useful to note that 32 * 64 / 2 = the size of your
	    drive in megabytes.  The division by 2 is to get from disk blocks
	    that are normally 512 bytes in size to Kbytes.</para>
	      
	  <para>Right.  All is well now?! No, it is not.  The system BIOS has
	    another quirk you might run into.  The number of cylinders of a
	    bootable hard disk cannot be greater than 1024.  Using the
	    translation above, this is a show-stopper for disks greater than 1
	    GB.  With disk capacities going up all the time this is causing
	    problems.</para>
	      
	  <para>Fortunately, the solution is simple: just use another
	    translation, e.g. with 128 heads instead of 32.  In most cases new
	    SCSI BIOS versions are available to upgrade older SCSI host
	    adapters.  Some newer adapters have an option, in the form of a
	    jumper or software setup selection, to switch the translation the
	    SCSI BIOS uses.</para>
	      
	  <para>It is very important that <emphasis>all</emphasis> operating
	    systems on the disk use the <emphasis>same translation</emphasis>
	    to get the right idea about where to find the relevant partitions.
	    So, when installing FreeBSD you must answer any questions about
	    heads/cylinders etc using the translated values your host adapter
	    uses.</para>
	      
	  <para>Failing to observe the translation issue might lead to
	    un-bootable systems or operating systems overwriting each others
	    partitions.  Using fdisk you should be able to see all
	    partitions.</para>
	      
	  <para>You might have heard some talk of <quote>lying</quote> devices?
	    Older FreeBSD kernels used to report the geometry of SCSI disks
	    when booting.  An example from one of my systems:</para>
	      
	  <screen>aha0 targ 0 lun 0: &lt;MICROP 1588-15MB1057404HSP4&gt;
sd0: 636MB (1303250 total sec), 1632 cyl, 15 head, 53 sec, bytes/sec 512</screen>

	  <para>Newer kernels usually do not report this information.
	    e.g.</para>

	  <screen>(bt0:0:0): "SEAGATE ST41651 7574" type 0 fixed SCSI 2
sd0(bt0:0:0): Direct-Access 1350MB (2766300 512 byte sectors)</screen>
		
	  <para>Why has this changed?</para>
	      
	  <para>This info is retrieved from the SCSI disk itself.  Newer disks
	    often use a technique called zone bit recording.  The idea is that
	    on the outer cylinders of the drive there is more space so more
	    sectors per track can be put on them.  This results in disks that
	    have more tracks on outer cylinders than on the inner cylinders
	    and, last but not least, have more capacity.  You can imagine that
	    the value reported by the drive when inquiring about the geometry
	    now becomes suspect at best, and nearly always misleading.  When
	    asked for a geometry, it is nearly always better to supply the
	    geometry used by the BIOS, or <emphasis>if the BIOS is never going
	      to know about this disk</emphasis>, (e.g. it is not a booting
	    disk) to supply a fictitious geometry that is convenient.</para>
	</sect3>

	<sect3>
	  <title>SCSI subsystem design</title>
	  
	  <para>FreeBSD uses a layered SCSI subsystem.  For each different
	    controller card a device driver is written.  This driver knows all
	    the intimate details about the hardware it controls.  The driver
	    has a interface to the upper layers of the SCSI subsystem through
	    which it receives its commands and reports back any status.</para>
	      
	  <para>On top of the card drivers there are a number of more generic
	    drivers for a class of devices.  More specific: a driver for tape
	    devices (abbreviation: st), magnetic disks (sd), CDROMs (cd) etc.
	    In case you are wondering where you can find this stuff, it all
	    lives in <filename>/sys/scsi</filename>.  See the man pages in
	    section 4 for more details.</para>
	      
	  <para>The multi level design allows a decoupling of low-level bit
	    banging and more high level stuff.  Adding support for another
	    piece of hardware is a much more manageable problem.</para>
	</sect3>

	<sect3>
	  <title>Kernel configuration</title>
	  
	  <para>Dependent on your hardware, the kernel configuration file must
	    contain one or more lines describing your host adapter(s).  This
	    includes I/O addresses, interrupts etc. Consult the man page for
	    your adapter driver to get more info. Apart from that, check out
	    <filename>/sys/i386/conf/LINT</filename> for an overview of a
	    kernel config file.  <filename>LINT</filename> contains every
	    possible option you can dream of.  It does
	    <emphasis>not</emphasis> imply <filename>LINT</filename> will
	    actually get you to a working kernel at all.</para>
	  
	  <para>Although it is probably stating the obvious: the kernel config
	    file should reflect your actual hardware setup.  So, interrupts,
	    I/O addresses etc must match the kernel config file.  During
	    system boot messages will be displayed to indicate whether the
	    configured hardware was actually found.</para>

	  <note>
	    <para>Note that most of the EISA/PCI drivers (namely
	      <devicename>ahb</devicename>, <devicename>ahc</devicename>,
	      <devicename>ncr</devicename> and <devicename>amd</devicename>
	      will automatically obtain the correct parameters from the host
	      adapters themselves at boot time; thus, you just need to write,
	      for instance, <literal>controller ahc0</literal>.</para>
	  </note>
	  
	  <para>An example loosely based on the FreeBSD 2.2.5-Release kernel
	    config  file <filename>LINT</filename> with some added comments
	    (between []):</para>
	      
	  <programlisting># SCSI host adapters: `aha', `ahb', `aic', `bt', `nca'
#
# aha: Adaptec 154x
# ahb: Adaptec 174x
# ahc: Adaptec 274x/284x/294x
# aic: Adaptec 152x and sound cards using the Adaptec AIC-6360 (slow!)
# amd: AMD 53c974 based SCSI cards (e.g., Tekram DC-390 and 390T)
# bt: Most Buslogic controllers
# nca: ProAudioSpectrum cards using the NCR 5380 or Trantor T130
# ncr: NCR/Symbios 53c810/815/825/875 etc based SCSI cards
# uha: UltraStore 14F and 34F
# sea: Seagate ST01/02 8 bit controller (slow!)
# wds: Western Digital WD7000 controller (no scatter/gather!).
#

[For an Adaptec AHA274x/284x/294x/394x etc controller]
controller	ahc0

[For an NCR/Symbios 53c875 based controller]
controller	ncr0

[For an Ultrastor adapter]
controller	uha0	at isa? port "IO_UHA0" bio irq ? drq 5 vector uhaintr

# Map SCSI buses to specific SCSI adapters
controller	scbus0	at ahc0
controller	scbus2 at ncr0
controller	scbus1  at uha0

# The actual SCSI devices
disk sd0 at scbus0 target 0 unit 0	[SCSI disk 0 is at scbus 0, LUN 0]
disk sd1 at scbus0 target 1             [implicit LUN 0 if omitted]
disk sd2 at scbus1 target 3             [SCSI disk on the uha0]
disk sd3 at scbus2 target 4             [SCSI disk on the ncr0]
tape st1 at scbus0 target 6             [SCSI tape at target 6]
device cd0 at scbus?                    [the first ever CDROM found, no wiring]</programlisting>
	      
	  <para>The example above tells the kernel to look for a ahc (Adaptec
	    274x) controller, then for an NCR/Symbios board, and so on.  The
	    lines following the controller specifications  tell the kernel to
	    configure specific devices but <emphasis>only</emphasis> attach
	    them when they match the target ID and LUN specified on the
	    corresponding bus.</para>
	      
	  <para>Wired down devices get <quote>first shot</quote> at the unit
	    numbers so the first non <quote>wired down</quote> device, is
	    allocated the unit number  one greater than the highest
	    <quote>wired down</quote> unit number for that kind of device.  So,
	    if you had a SCSI tape at target ID 2 it would be configured as
	    st2, as the tape at target ID 6 is wired down to unit number
	    1.</para>

	  <note>
	    <para>Wired down devices need not be found to get their unit
	      number.  The unit number for a wired down device is reserved for
	      that device, even if it is turned off at boot time.  This allows
	      the device to be turned on and brought on-line at a later time,
	      without rebooting.  Notice that a device's unit number has
	      <emphasis>no</emphasis> relationship with its target ID on  the
	      SCSI bus.</para>
	  </note>
	  
	  <para>Below is another example of a kernel config file as used by
	    FreeBSD version &lt; 2.0.5.  The difference with the first example
	    is that devices are not <quote>wired down</quote>.  <quote>Wired
	    down</quote> means that you specify which SCSI target belongs to
	    which device.</para>
	      
	  <para>A kernel built to the config file below will attach  the first
	    SCSI disk it finds to sd0, the second disk to sd1 etc. If you ever
	    removed or added a disk, all other devices of the same type (disk
	    in this case) would <quote>move around</quote>.  This implies you have to
	    change <filename>/etc/fstab</filename> each time.</para>
	      
	  <para>Although the old style still works, you  are
	    <emphasis>strongly</emphasis> recommended to use this new feature.
	    It will save you a lot of grief whenever you shift your hardware
	    around on the SCSI buses.  So, when you re-use your old trusty
	    config file after upgrading from a pre-FreeBSD2.0.5.R system check
	    this out.</para>
	  
	  <programlisting>[driver for Adaptec 174x]
controller      ahb0 at isa? bio irq 11 vector ahbintr

[for Adaptec 154x]
controller      aha0    at isa? port "IO_AHA0" bio irq 11 drq 5 vector ahaintr

[for Seagate ST01/02]
controller      sea0    at isa? bio irq 5 iomem 0xc8000 iosiz 0x2000 vector seaintr

controller      scbus0

device          sd0     [support for 4 SCSI harddisks, sd0 up sd3]
device          st0	[support for 2 SCSI tapes]

[for the CDROM]
device          cd0     #Only need one of these, the code dynamically grows</programlisting>
	      
	  <para>Both examples support SCSI disks.  If during boot more devices
	    of a specific type (e.g. sd disks) are found than are configured
	    in the booting kernel, the system will simply allocate more
	    devices, incrementing the unit number starting at the last number
	    <quote>wired down</quote>.  If there are no <quote>wired
	    down</quote> devices then counting starts at unit 0.</para>
	      
	  <para>Use <command>man 4 scsi</command> to check for the latest info
	    on the SCSI subsystem.  For more detailed info on host adapter
	    drivers use e.g., <command>man 4 ahc</command> for info on the
	    Adaptec 294x driver.</para>
	</sect3>

	<sect3>
	  <title>Tuning your SCSI kernel setup</title>
	  
	  <para>Experience has shown that some devices are slow to respond to
	    INQUIRY commands after a SCSI bus reset (which happens at boot
	    time).  An INQUIRY command is sent by the kernel on boot to see
	    what kind of device (disk, tape, CDROM etc.) is connected to a
	    specific target ID.  This process is called device probing by the
	    way.</para>
	      
	  <para>To work around the <quote>slow response</quote> problem, FreeBSD allows a
	    tunable delay time before the SCSI devices are probed following a
	    SCSI bus reset.  You can set this delay time in your kernel
	    configuration file using a line like:</para>
	      
	  <programlisting>options         SCSI_DELAY=15         #Be pessimistic about Joe SCSI device</programlisting>

	  <para>This line sets the delay time to 15 seconds.  On my own system
	    I had to use 3 seconds minimum to get my trusty old CDROM drive
	    to be recognized.  Start with a high value (say 30 seconds or so)
	    when you have problems  with device recognition.  If this helps,
	    tune it back until it just stays working.</para>
	</sect3>

	<sect3 id="scsi-rogue-devices">
	  <title>Rogue SCSI devices</title>
	      
	  <para>Although the SCSI standard tries to be complete and concise,
	    it is a complex standard and implementing things correctly is no
	    easy task.  Some vendors do a better job then others.</para>
	      
	  <para>This is exactly where the <quote>rogue</quote> devices come
	    into view. Rogues are devices that are recognized by the FreeBSD
	    kernel as behaving slightly (...) non-standard.  Rogue devices are
	    reported by the kernel when booting.  An example for two of my
	    cartridge tape units:</para>
	  
	  <screen>Feb 25 21:03:34 yedi /kernel: ahb0 targ 5 lun 0: &lt;TANDBERG TDC 3600       -06:&gt;
Feb 25 21:03:34 yedi /kernel: st0: Tandberg tdc3600 is a known rogue

Mar 29 21:16:37 yedi /kernel: aha0 targ 5 lun 0: &lt;ARCHIVE VIPER 150  21247-005&gt;
Mar 29 21:16:37 yedi /kernel: st1: Archive  Viper 150 is a known rogue </screen>
	      
	  <para>For instance, there are devices that respond to all LUNs on a
	    certain target ID, even if they are actually only one device.  It
	    is easy to see that the kernel might be fooled into believing that
	    there are 8 LUNs at that particular target ID. The confusion this
	    causes is left as an exercise to the reader.</para>
	      
	  <para>The SCSI subsystem of FreeBSD recognizes devices with bad
	    habits by looking at the INQUIRY response they send when probed.
	    Because the INQUIRY response also includes the version number of
	    the device  firmware, it is even possible that for different
	    firmware versions different workarounds are used. See e.g.
	    <filename>/sys/scsi/st.c</filename> and
	    <filename>/sys/scsi/scsiconf.c</filename> for more info on how
	    this is done.</para>
	      
	  <para>This scheme works fine, but keep in mind that it of course
	    only works for devices that are known to be weird.  If you are the
	    first to connect your bogus Mumbletech SCSI CDROM you might be
	    the one that has to define which workaround is needed.</para>
	      
	  <para>After you got your Mumbletech working, please send the
	    required workaround to the FreeBSD development team for inclusion
	    in the next release of FreeBSD.  Other Mumbletech owners will be
	    grateful  to you.</para>
	</sect3>

	<sect3>
	  <title>Multiple LUN devices</title>
	  
	  <para>In some cases you come across devices that use multiple
	    logical units (LUNs) on a single SCSI ID.  In most cases FreeBSD
	    only probes devices for LUN 0.  An example are so called bridge
	    boards that connect 2 non-SCSI hard disks to a SCSI bus (e.g. an
	    Emulex MD21 found in old Sun systems).</para>
	      
	  <para>This means that any devices with LUNs != 0 are not normally
	    found during device probe on system boot.  To work around this
	    problem you must add an appropriate entry in /sys/scsi/scsiconf.c
	    and rebuild your kernel.</para>
	      
	  <para>Look for a struct that is initialized like below:</para>

	  <programlisting>{
        T_DIRECT, T_FIXED, "MAXTOR", "XT-4170S", "B5A",
        "mx1", SC_ONE_LU
}</programlisting>
	      
	  <para>For you Mumbletech BRIDGE2000 that has more than one LUN, acts
	    as a SCSI disk and has firmware revision 123 you would add
	    something like:</para>
	      
	  <programlisting>{
        T_DIRECT, T_FIXED, "MUMBLETECH", "BRIDGE2000", "123",
        "sd", SC_MORE_LUS
}</programlisting>
	      
	  <para>The kernel on boot scans the inquiry data it receives against
	    the table and acts accordingly.  See the source for more
	    info.</para>
	</sect3>

	<sect3>
	  <title>Tagged command queuing</title>
	  
	  <para>Modern SCSI devices, particularly magnetic disks,
	    support what is called tagged command queuing (TCQ).</para>
	  
	  <para>In a nutshell, TCQ allows the device to have multiple I/O
	    requests outstanding at the same time.  Because the device is
	    intelligent, it can optimize its operations (like head
	    positioning) based on its own request queue.  On  SCSI devices
	    like RAID (Redundant Array of Independent Disks) arrays the TCQ
	    function is indispensable to take advantage of the device's
	    inherent parallelism.</para>
	      
	  <para>Each I/O request is uniquely identified by a <quote>tag</quote>
	    (hence the name tagged command queuing) and this tag is used by
	    FreeBSD to see which I/O in the device drivers queue is reported
	    as complete by the device.</para>
	      
	  <para>It should be noted however that TCQ requires device driver
	    support and that some devices implemented it <quote>not quite
	    right</quote> in their firmware.  This problem bit me once, and it
	    leads to highly mysterious problems.  In such cases, try to
	    disable TCQ.</para>
	</sect3>

	<sect3>
	  <title>Busmaster host adapters</title>
	  
	  <para>Most, but not all, SCSI host adapters are bus mastering
	    controllers.  This means that they can do I/O on their own without
	    putting load onto the host CPU for data movement.</para>
	      
	  <para>This is of course an advantage for a multitasking operating
	    system like FreeBSD.  It must be noted however that there might be
	    some rough edges.</para>
	      
	  <para>For instance an Adaptec 1542 controller can be set to use
	    different transfer speeds on the host bus (ISA or AT in this
	    case).  The controller is settable to different rates because not
	    all motherboards can handle the higher speeds.  Problems like
	    hang-ups, bad data etc might be the result of using a higher data
	    transfer rate then your motherboard can stomach.</para>
	      
	  <para>The solution is of course obvious: switch to a lower data
	    transfer rate and try if that works better.</para>
	      
	  <para>In the case of a Adaptec 1542, there is an option that can be
	    put into the kernel config file to allow dynamic determination of
	    the right, read: fastest feasible, transfer rate.  This option is
	    disabled by default:</para>
	      
	  <programlisting>options        "TUNE_1542"             #dynamic tune of bus DMA speed</programlisting>
	      
	  <para>Check the man pages for the host adapter that you use.  Or
	    better still, use the ultimate documentation (read: driver
	    source).</para>
	</sect3>
      </sect2>
      
      <sect2>
	<title>Tracking down problems</title>

	<para>The following list is an attempt to give a guideline for the
	  most common SCSI problems and their solutions.  It is by no means
	  complete.</para>
	    
	<itemizedlist>
	  <listitem>
	    <para>Check for loose connectors and cables.</para>
	  </listitem>
	  
	  <listitem>
	    <para>Check and double check the location and number of your
	      terminators.</para>
	  </listitem>
	  
	  <listitem>
	    <para>Check if your bus has at least one supplier of terminator
	      power (especially with external terminators.</para>
	  </listitem>
	  
	  <listitem>
	    <para>Check if no double target IDs are used.</para>
	  </listitem>
	  
	  <listitem>
	    <para>Check if all devices to be used are powered up.</para>
	  </listitem>
	  
	  <listitem>
	    <para>Make a minimal bus config with as little devices as
	      possible.</para>
	  </listitem>
	  
	  <listitem>
	    <para>If possible, configure your host adapter to use slow bus
	      speeds.</para>
	  </listitem>
	  
	  <listitem>
	    <para>Disable tagged command queuing to make things as simple as
	      possible (for a NCR host adapter based system see man
	      ncrcontrol)</para>
	  </listitem>
	  
	  <listitem>
	    <para>If you can compile a kernel, make one with the
	      <literal>SCSIDEBUG</literal> option, and try accessing the
	      device with debugging turned on for that device.  If your device
	      does not even probe at startup, you may have to define the
	      address of the device that is failing, and the desired debug
	      level in <filename>/sys/scsi/scsidebug.h</filename>. If it
	      probes but just does not work, you can use the
		    &man.scsi.8; command to dynamically set a debug level to
	      it in a running kernel (if <literal>SCSIDEBUG</literal> is
	      defined).  This will give you <emphasis>copious</emphasis>
	      debugging output with which to confuse the gurus. See
	      <command>man 4 scsi</command> for more exact information.  Also
	      look at <command>man 8 scsi</command>.</para>
	  </listitem>
	</itemizedlist>
      </sect2>
      
      <sect2 id="scsi-further-reading">
	<title>Further reading</title>

	<para>If you intend to do some serious SCSI hacking, you might want to
	  have the official standard at hand:</para>
	    
	<para>Approved American National Standards can be purchased from
	  ANSI at
	  
	  <address>
	    <otheraddr>13th Floor</otheraddr>
	    <street>11 West 42nd Street</street>
	    <city>New York</city>
	    <state>NY</state> <postcode>10036</postcode>
	    Sales Dept: <phone>(212) 642-4900</phone>
	  </address>
	</para>

	<para>You can also buy many ANSI
	  standards and most committee draft documents from Global
	  Engineering Documents,

	  <address>
	    <street>15 Inverness Way East</street>
	    <city>Englewood</city>
	    <state>CO</state>, <postcode>80112-5704</postcode>
	    Phone: <phone>(800) 854-7179</phone>
	    Outside USA and Canada: <phone>(303) 792-2181</phone>
	    Fax: <fax>(303) 792- 2192</fax>
	  </address>
	</para>

	<para>Many X3T10 draft documents are available electronically on the
	  SCSI BBS (719-574-0424) and on the <hostid
	    role="fqdn">ncrinfo.ncr.com</hostid> anonymous FTP site.</para>
	    
	<para>Latest X3T10 committee documents are:</para>

	<itemizedlist>
	  <listitem>
	    <para>AT Attachment (ATA or IDE) [X3.221-1994]
	      (<emphasis>Approved</emphasis>)</para>
	  </listitem>
	  
	  <listitem>
	    <para>ATA Extensions (ATA-2) [X3T10/948D Rev 2i]</para>
	  </listitem>
	  
	  <listitem>
	    <para>Enhanced Small Device Interface (ESDI)
	      [X3.170-1990/X3.170a-1991]
	      (<emphasis>Approved</emphasis>)</para>
	  </listitem>
	  
	  <listitem>
	    <para>Small Computer System Interface &mdash; 2 (SCSI-2)
	      [X3.131-1994] (<emphasis>Approved</emphasis>)</para>
	  </listitem>
	  
	  <listitem>
	    <para>SCSI-2 Common Access Method Transport and SCSI Interface
	      Module (CAM)  [X3T10/792D Rev 11]</para>
	  </listitem>
	</itemizedlist>

	<para>Other publications that might provide you with additional
	  information are:</para>

	<itemizedlist>
	  <listitem>
	    <para><quote>SCSI: Understanding the Small Computer System
	      Interface</quote>, written by NCR  Corporation.  Available from:
	      Prentice Hall, Englewood Cliffs, NJ, 07632 Phone: (201) 767-5937
	      ISBN 0-13-796855-8</para>
	  </listitem>
	  
	  <listitem>
	    <para><quote>Basics of SCSI</quote>, a SCSI tutorial written by
	      Ancot Corporation Contact Ancot for availability information at:
	      Phone: (415) 322-5322  Fax: (415) 322-0455</para>
	  </listitem>
	  
	  <listitem>
	    <para><quote>SCSI Interconnection Guide Book</quote>, an AMP
	      publication (dated 4/93, Catalog  65237) that lists the various
	      SCSI connectors and suggests cabling schemes.  Available from
	      AMP at (800) 522-6752 or (717) 564-0100</para>
	  </listitem>
	  
	  <listitem>
	    <para><quote>Fast Track to SCSI</quote>, A Product Guide written by
	      Fujitsu.  Available from: Prentice Hall, Englewood Cliffs, NJ,
	      07632 Phone: (201) 767-5937 ISBN 0-13-307000-X</para>
	  </listitem>
	  
	  <listitem>
	    <para><quote>The SCSI Bench Reference</quote>, <quote>The SCSI
	      Encyclopedia</quote>, and the <quote>SCSI Tutor</quote>, ENDL
	      Publications, 14426 Black Walnut Court, Saratoga CA, 95070
	      Phone: (408) 867-6642</para>
	  </listitem>
	  
	  <listitem>
	    <para><quote>Zadian SCSI Navigator</quote> (quick ref. book) and
	      <quote>Discover the Power of SCSI</quote>  (First book along with
	      a one-hour video and tutorial book), Zadian Software, Suite 214,
	      1210 S. Bascom Ave., San Jose, CA 92128, (408) 293-0800</para>
	  </listitem>
	</itemizedlist>

	<para>On Usenet the newsgroups <ulink
	    url="news:comp.periphs.scsi">comp.periphs.scsi</ulink> and <ulink
	    url="news:comp.periphs">comp.periphs</ulink> are noteworthy places
	  to look for more info.  You can also find the SCSI-Faq there, which
	  is posted periodically.</para>

	<para>Most major SCSI device and host adapter suppliers operate FTP
	  sites and/or BBS systems.  They may be valuable sources of
	  information about the devices you own.</para>
      </sect2>
    </sect1>
    
    <sect1 id="hw-storage-controllers">
      <title>* Disk/tape controllers</title>
      
      <sect2>
	<title>* SCSI</title>

	<para></para>
      </sect2>
      
      <sect2>
	<title>* IDE</title>

	<para></para>
      </sect2>
      
      <sect2>
	<title>* Floppy</title>

	<para></para>
      </sect2>
    </sect1>
    
    <sect1>
      <title>Hard drives</title>
      
      <sect2>
	<title>SCSI hard drives</title>

	<para><emphasis>Contributed by &a.asami;.  17 February
	    1998.</emphasis></para>
	    
	<para>As mentioned in the <link linkend="scsi">SCSI</link> section,
	  virtually all SCSI hard drives sold today are SCSI-2 compliant and
	  thus will work fine as long as you connect them to a supported SCSI
	  host adapter.  Most problems people encounter are either due to
	  badly designed cabling (cable too long, star topology, etc.),
	  insufficient termination, or defective parts. Please refer to the
	  <link linkend="scsi">SCSI</link> section first if your SCSI hard
	  drive is not working.  However, there are a couple of things you may
	  want to take into account before you purchase SCSI hard drives for
	  your system.</para>

	<sect3>
	  <title>Rotational speed</title>
	  
	  <para>Rotational speeds of SCSI drives sold today range from around
	    4,500RPM to 10,000RPM.  Most of them are either 5,400RPM or
	    7,200RPM.  Even though the 7,200RPM drives can generally transfer
	    data faster, they run considerably hotter than their 5,400RPM
	    counterparts.  A large fraction of today's disk drive malfunctions
	    are heat-related.  If you do not have very good cooling in your PC
	    case, you may want to stick with 5,400RPM or slower drives.</para>
	      
	  <para>Note that newer drives, with higher areal recording densities,
	    can deliver much more bits per rotation than older ones.  Today's
	    top-of-line 5,400RPM drives can sustain a throughput comparable to
	    7,200RPM drives of one or two model generations ago.  The number
	    to find on the spec sheet for bandwidth is <quote>internal data
	    (or transfer) rate</quote>.  It is usually in megabits/sec so
	    divide it by 8 and you will get the rough approximation of how much
	    megabytes/sec you can get out of the drive.</para>
	      
	  <para>(If you are a speed maniac and want a 10,000RPM drive for your
	    cute little PC, be my guest; however, those drives become
	    extremely hot.  Do not even think about it if you do not have a fan
	    blowing air <emphasis>directly at</emphasis> the drive or a
	    properly ventilated disk enclosure.)</para>
	      
	  <para>Obviously, the latest 10,000RPM drives and 7,200RPM drives can
	    deliver more data than the latest 5,400RPM drives, so if absolute
	    bandwidth is the necessity for your applications, you have little
	    choice but to get the faster drives.  Also, if you need low
	    latency, faster drives are better; not only do they usually have
	    lower average seek times, but also the rotational delay is one
	    place where slow-spinning drives can never beat a faster one.
	    (The average rotational latency is half the time it takes to
	    rotate the drive once; thus, it is 3 milliseconds for 10,000RPM
	    drives, 4.2ms for 7,200RPM drives and 5.6ms for 5,400RPM drives.)
	    Latency is seek time plus rotational delay. Make sure you
	    understand whether you need low latency or more accesses per
	    second, though; in the latter case (e.g., news servers), it may
	    not be optimal to purchase one big fast drive.  You can achieve
	    similar or even better results by using the ccd (concatenated
	    disk) driver to create a striped disk array out of multiple slower
	    drives for comparable overall cost.</para>
	      
	  <para>Make sure you have adequate air flow around the drive,
	    especially if you are going to use a fast-spinning drive.  You
	    generally need at least 1/2&rdquo; (1.25cm) of spacing above and below a
	    drive.  Understand how the air flows through your PC case.  Most
	    cases have the power supply suck the air out of the back.  See
	    where the air flows in, and put the drive where it will have the
	    largest volume of cool air flowing around it. You may need to seal
	    some unwanted holes or add a new fan for effective cooling.</para>
	      
	  <para>Another consideration is noise.  Many 7,200 or faster drives
	    generate a high-pitched whine which is quite unpleasant to most
	    people.  That, plus the extra fans often required for cooling, may
	    make 7,200 or faster drives unsuitable for some office and home
	    environments.</para>
	</sect3>

	<sect3>
	  <title>Form factor</title>
	  
	  <para>Most SCSI drives sold today are of 3.5&rdquo; form factor.  They
	    come in two different heights; 1.6&rdquo; (<quote>half-height</quote>) or
	    1&rdquo; (<quote>low-profile</quote>).  The half-height drive is the same
	    height as a CDROM drive.  However, do not forget the spacing rule
	    mentioned in the previous section.  If you have three standard
	    3.5&rdquo; drive bays, you will not be able to put three half-height
	    drives in there (without frying them, that is).</para>
	</sect3>

	<sect3>
	  <title>Interface</title>
	  
	  <para>The majority of SCSI hard drives sold today are Ultra or
	    Ultra-wide SCSI.  The maximum bandwidth of Ultra SCSI is 20MB/sec,
	    and Ultra-wide SCSI is 40MB/sec.  There is no difference in max
	    cable length between Ultra and Ultra-wide; however, the more
	    devices you have on the same bus, the sooner you will start having
	    bus integrity problems.  Unless you have a well-designed disk
	    enclosure, it is not easy to make more than 5 or 6 Ultra SCSI
	    drives work on a single bus.</para>
	      
	  <para>On the other hand, if you need to connect many drives, going
	    for Fast-wide SCSI may not be a bad idea.  That will have the same
	    max bandwidth as Ultra (narrow) SCSI, while electronically it is
	    much easier to get it <quote>right</quote>.  My advice would be: if
	    you want to connect many disks, get wide SCSI drives; they usually
	    cost a little more but it may save you down the road.  (Besides,
	    if you can not afford the cost difference, you should not be building
	    a disk array.)</para>
	      
	  <para>There are two variant of wide SCSI drives; 68-pin and 80-pin
	    SCA (Single Connector Attach).  The SCA drives do not have a
	    separate 4-pin power connector, and also read the SCSI ID settings
	    through the 80-pin connector.  If you are really serious about
	    building a large storage system, get SCA drives and a good SCA
	    enclosure (dual power supply with at least one extra fan).  They
	    are more electronically sound than 68-pin counterparts because
	    there is no <quote>stub</quote> of the SCSI bus inside the disk
	    canister as in arrays built from 68-pin drives.  They are easier
	    to install too (you just need to screw the drive in the canister,
	    instead of trying to squeeze in your fingers in a tight place to
	    hook up all the little cables (like the SCSI ID and disk activity
	    LED lines).</para>
	</sect3>
      </sect2>
      
      <sect2>
	<title>* IDE hard drives</title>

	<para></para>
      </sect2>
    </sect1>
    
    <sect1>
      <title>Tape drives</title>
      
      <para><emphasis>Contributed by &a.jmb;.  2 July
	  1996.</emphasis></para>
      
      <sect2>
	<title>General tape access commands</title>

	<para>&man.mt.1; provides generic access to the tape drives.  Some of
	  the more common commands are <command>rewind</command>,
	  <command>erase</command>, and <command>status</command>.  See the
	    &man.mt.1; manual page for a detailed description.</para>
      </sect2>
      
      <sect2>
	<title>Controller Interfaces</title>

	<para>There are several different interfaces that support tape drives.
	  The interfaces are SCSI, IDE, Floppy and Parallel Port. A wide
	  variety of tape drives are available for these interfaces.
	  Controllers are discussed in <link
	    linkend="hw-storage-controllers">Disk/tape
	    controllers</link>.</para>
      </sect2>
      
      <sect2>
	<title>SCSI drives</title>

	<para>The &man.st.4; driver provides support for 8mm (Exabyte), 4mm
	  (DAT: Digital Audio Tape), QIC (Quarter-Inch Cartridge), DLT
	  (Digital Linear Tape), QIC Mini cartridge and 9-track (remember the
	  big reels that you see spinning in Hollywood computer rooms) tape
	  drives.  See the &man.st.4; manual page for a detailed
	  description.</para>

	<para>The drives listed below are currently being used by members of
	  the FreeBSD community.  They are not the only drives that will work
	  with FreeBSD.  They just happen to be the ones that we use.</para>

	<sect3>
	  <title>4mm (DAT: Digital Audio Tape)</title>
	  
	  <para><link linkend="hw-storage-python-28454">Archive Python
	      28454</link></para>

	  <para><link linkend="hw-storage-python-04687">Archive Python
	      04687</link></para>
	  
	  <para><link linkend="hw-storage-hp1533a">HP C1533A</link></para>
	      
	  <para><link linkend="hw-storage-hp1534a">HP C1534A</link></para>
	      
	  <para><link linkend="hw-storage-hp35450a">HP 35450A</link></para>
	      
	  <para><link linkend="hw-storage-hp35470a">HP 35470A</link></para>
	      
	  <para><link linkend="hw-storage-hp35480a">HP 35480A</link></para>
	      
	  <para><link linkend="hw-storage-sdt5000">SDT-5000</link></para>
	      
	  <para><link linkend="hw-storage-wangtek6200">Wangtek
	      6200</link></para>
	</sect3>

	<sect3>
	  <title>8mm (Exabyte)</title>
	  
	  <para><link linkend="hw-storage-exb8200">EXB-8200</link></para>
	  
	  <para><link linkend="hw-storage-exb8500">EXB-8500</link></para>
	  
	  <para><link linkend="hw-storage-exb8505">EXB-8505</link></para>
	</sect3>

	<sect3>
	  <title>QIC (Quarter-Inch Cartridge)</title>
	  
	  <para><link linkend="hw-storage-anaconda">Archive Anaconda
	      2750</link></para>
	      
	  <para><link linkend="hw-storage-viper60">Archive Viper
	      60</link></para>
	      
	  <para><link linkend="hw-storage-viper150">Archive Viper
	      150</link></para>
	      
	  <para><link linkend="hw-storage-viper2525">Archive Viper
	      2525</link></para>
	      
	  <para><link linkend="hw-storage-tandberg3600">Tandberg TDC
	      3600</link></para>

	  <para><link linkend="hw-storage-tandberg3620">Tandberg TDC
	      3620</link></para>
	    
	  <para><link linkend="hw-storage-tandberg3800">Tandberg TDC
	      3800</link></para>
	      
	  <para><link linkend="hw-storage-tandberg4222">Tandberg TDC
	      4222</link></para>
	      
	  <para><link linkend="hw-storage-wangtek5525es">Wangtek
	      5525ES</link></para>
	</sect3>

	<sect3>
	  <title>DLT (Digital Linear Tape)</title>
	  
	  <para><link linkend="hw-storage-dectz87">Digital TZ87</link></para>
	</sect3>

	<sect3>
	  <title>Mini-Cartridge</title>
	  
	  <para><link linkend="hw-storage-ctms3200">Conner CTMS
	      3200</link></para>
	      
	  <para><link linkend="hw-storage-exb2501">Exabyte 2501</link></para>
	</sect3>

	<sect3>
	  <title>Autoloaders/Changers</title>
	  
	  <para><link linkend="hw-storage-hp1553a">Hewlett-Packard HP C1553A
	      Autoloading DDS2</link></para>
	</sect3>
      </sect2>
      
      <sect2>
	<title>* IDE drives</title>

	<para></para>
      </sect2>
      
      <sect2>
	<title>Floppy drives</title>

	<para><link linkend="hw-storage-conner420r">Conner 420R</link></para>
      </sect2>
      
      <sect2>
	<title>* Parallel port drives</title>

	<para></para>
      </sect2>
      
      <sect2>
	<title>Detailed Information</title>

	<sect3 id="hw-storage-anaconda">
	  <title>Archive Anaconda 2750</title>
	  
	  <para>The boot message identifier for this drive is <literal>ARCHIVE
	      ANCDA 2750 28077 -003 type 1 removable SCSI 2</literal></para>
	  
	  <para>This is a QIC tape drive.</para>
	  
	  <para>Native capacity is 1.35GB when using QIC-1350 tapes.  This
	    drive will read and write QIC-150 (DC6150), QIC-250 (DC6250), and
	    QIC-525 (DC6525) tapes as well.</para>
	      
	  <para>Data transfer rate is 350kB/s using &man.dump.8;.
	    Rates of 530kB/s have been reported when using
	    Amanda</para>

	  <para>Production of this drive has been discontinued.</para>
	  
	  <para>The SCSI bus connector on this tape drive is reversed from
	    that on most other SCSI devices.  Make sure that you have enough
	    SCSI cable to twist the cable one-half turn before and after the
	    Archive Anaconda tape drive, or turn your other SCSI devices
	    upside-down.</para>
	  
	  <para>Two kernel code changes are required to use this drive. This
	    drive will not work as delivered.</para>
	      
	  <para>If you have a SCSI-2 controller, short jumper 6. Otherwise,
	    the drive behaves are a SCSI-1 device.  When operating as a SCSI-1
	    device, this drive, <quote>locks</quote> the SCSI bus during some
	    tape operations, including: fsf, rewind, and rewoffl.</para>
	      
	  <para>If you are using the NCR SCSI controllers, patch the file
	    <filename>/usr/src/sys/pci/ncr.c</filename> (as shown below).
	    Build and install a new kernel.</para>
	      
	  <programlisting>*** 4831,4835 ****
                };
        
!               if (np-&gt;latetime&gt;4) {
                        /*
                        **      Although we tried to wake it up,
--- 4831,4836 ----
                };

!               if (np-&gt;latetime&gt;1200) {
                        /*
                        **      Although we tried to wake it up,</programlisting>
	      
	  <para>Reported by: &a.jmb;</para>
	</sect3>

	<sect3 id="hw-storage-python-28454">
	  <title>Archive Python 28454</title>
	  
	  <para>The boot message identifier for this drive is <literal>ARCHIVE
	      Python 28454-XXX4ASB</literal> <literal>type 1 removable SCSI
	      2</literal> <literal>density code 0x8c, 512-byte
	      blocks</literal></para>
	      
	  <para>This is a DDS-1 tape drive.</para>
	      
	  <para>Native capacity is 2.5GB on 90m tapes.</para>
	  
	  <para>Data transfer rate is XXX.</para>
	  
	  <para>This drive was repackaged by Sun Microsystems as model
	    595-3067.</para>
	      
	  <para>Reported by: Bob Bishop <email>rb@gid.co.uk</email></para>
	  
	  <para>Throughput is in the 1.5 MByte/sec range, however this will
	    drop if the disks and tape drive are on the same SCSI
	    controller.</para>

	  <para>Reported by: Robert E. Seastrom
	    <email>rs@seastrom.com</email></para>
	</sect3>

	<sect3 id="hw-storage-python-04687">
	  <title>Archive Python 04687</title>

	  <para>The boot message identifier for this drive is <literal>ARCHIVE 
	      Python 04687-XXX 6580</literal> <literal>Removable Sequential
	      Access SCSI-2 device</literal></para>

	  <para>This is a DAT-DDS-2 drive.</para>

	  <para>Native capacity is 4GB when using 120m tapes.</para>

	  <para>This drive supports hardware data compression.  Switch 4
	    controls MRS (Media Recognition System).  MRS tapes have stripes
	    on the transparent leader.  Switch 4 <emphasis>off</emphasis>
	    enables MRS, <emphasis>on</emphasis> disables MRS.</para>

	  <para>Parity is controlled by switch 5.  Switch 5
	    <emphasis>on</emphasis> to enable parity control.  Compression is
	    enabled with Switch 6 <emphasis>off</emphasis>.  It is possible to 
	    override compression with the <literal>SCSI MODE SELECT</literal>
	    command (see &man.mt.1;).</para>

	  <para>Data transfer rate is 800kB/s.</para>
	</sect3>

	<sect3 id="hw-storage-viper60">
	  <title>Archive Viper 60</title>
	  
	  <para>The boot message identifier for this drive is <literal>ARCHIVE
	      VIPER 60 21116 -007</literal> <literal>type 1 removable SCSI
	      1</literal></para>
	      
	  <para>This is a QIC tape drive.</para>
	  
	  <para>Native capacity is 60MB.</para>
	  
	  <para>Data transfer rate is XXX.</para>
	  
	  <para>Production of this drive has been discontinued.</para>
	  
	  <para>Reported by: Philippe Regnauld
	    <email>regnauld@hsc.fr</email></para>
	</sect3>

	<sect3 id="hw-storage-viper150">
	  <title>Archive Viper 150</title>
	  
	  <para>The boot message identifier for this drive is <literal>ARCHIVE
	      VIPER 150 21531 -004</literal> <literal>Archive Viper 150 is a
	      known rogue</literal> <literal>type 1 removable SCSI
	      1</literal>.  A multitude of firmware revisions exist for this
	    drive.  Your drive may report different numbers (e.g
	    <literal>21247 -005</literal>.</para>
	      
	  <para>This is a QIC tape drive.</para>
	  
	  <para>Native capacity is 150/250MB.  Both 150MB (DC6150) and 250MB
	    (DC6250) tapes have the recording format.  The 250MB tapes are
	    approximately 67% longer than the 150MB tapes.  This drive can
	    read 120MB tapes as well.  It can not write 120MB tapes.</para>
	      
	  <para>Data transfer rate is 100kB/s</para>
	  
	  <para>This drive reads and writes DC6150 (150MB) and DC6250 (250MB)
	    tapes.</para>
	      
	  <para>This drives quirks are known and pre-compiled into the scsi
	    tape device driver (&man.st.4;).</para>
	      
	  <para>Under FreeBSD 2.2-CURRENT, use <command>mt blocksize
	      512</command> to set the blocksize.  (The particular drive had
	    firmware revision 21247 -005.  Other firmware revisions may behave
	    differently) Previous versions of FreeBSD did not have this
	    problem.</para>
	      
	  <para>Production of this drive has been discontinued.</para>
	  
	  <para>Reported by: Pedro A M Vazquez
	    <email>vazquez@IQM.Unicamp.BR</email></para>
	  
	  <para>&a.msmith;</para>
	</sect3>
	    
	<sect3 id="hw-storage-viper2525">
	  <title>Archive Viper 2525</title>
	  
	  <para>The boot message identifier for this drive is <literal>ARCHIVE
	      VIPER 2525 25462 -011</literal> <literal>type 1 removable SCSI
	      1</literal></para>
	  
	  <para>This is a QIC tape drive.</para>
	  
	  <para>Native capacity is 525MB.</para>
	  
	  <para>Data transfer rate is 180kB/s at 90 inches/sec.</para>
	  
	  <para>The drive reads QIC-525, QIC-150, QIC-120 and QIC-24 tapes.
	    Writes QIC-525, QIC-150, and QIC-120.</para>
	      
	  <para>Firmware revisions prior to <literal>25462 -011</literal> are
	    bug ridden and will not function properly.</para>
	  
	  <para>Production of this drive has been discontinued.</para>
	</sect3>

	<sect3 id="hw-storage-conner420r">
	  <title>Conner 420R</title>
	  
	  <para>The boot message identifier for this drive is <literal>Conner
	      tape</literal>.</para>
	      
	  <para>This is a floppy controller, mini cartridge tape drive.</para>
	      
	  <para>Native capacity is XXXX</para>
	  
	  <para>Data transfer rate is XXX</para>
	  
	  <para>The drive uses QIC-80 tape cartridges.</para>
	  
	  <para>Reported by: Mark Hannon
	    <email>mark@seeware.DIALix.oz.au</email></para>
	</sect3>

	<sect3 id="hw-storage-ctms3200">
	  <title>Conner CTMS 3200</title>
	      
	  <para>The boot message identifier for this drive is <literal>CONNER
	      CTMS 3200 7.00</literal> <literal>type 1 removable SCSI
	      2</literal>.</para>
	      
	  <para>This is a mini cartridge tape drive.</para>
	  
	  <para>Native capacity is XXXX</para>
	  
	  <para>Data transfer rate is XXX</para>
	  
	  <para>The drive uses QIC-3080 tape cartridges.</para>
	  
	  <para>Reported by: Thomas S. Traylor
	    <email>tst@titan.cs.mci.com</email></para>
	</sect3>

	<sect3 id="hw-storage-dectz87">
	  <title><ulink
	      url="http://www.digital.com/info/Customer-Update/931206004.txt.html">DEC TZ87</ulink></title>
	  
	  <para>The boot message identifier for this drive is <literal>DEC
	      TZ87 (C) DEC 9206</literal> <literal>type 1 removable SCSI
	      2</literal> <literal>density code 0x19</literal></para>
	      
	  <para>This is a DLT tape drive.</para>
	  
	  <para>Native capacity is 10GB.</para>
	  
	  <para>This drive supports hardware data compression.</para>
	  
	  <para>Data transfer rate is 1.2MB/s.</para>
	  
	  <para>This drive is identical to the Quantum DLT2000.  The drive
	    firmware can be set to emulate several well-known drives,
	    including an Exabyte 8mm drive.</para>
	      
	  <para>Reported by: &a.wilko;</para>
	</sect3>

	<sect3 id="hw-storage-exb2501">
	  <title><ulink
	      url="http://www.Exabyte.COM:80/Products/Minicartridge/2501/Rfeatures.html">Exabyte EXB-2501</ulink></title>
	      
	  <para>The boot message identifier for this drive is <literal>EXABYTE
	      EXB-2501</literal></para>
	      
	  <para>This is a mini-cartridge tape drive.</para>
	      
	  <para>Native capacity is 1GB when using MC3000XL
	    mini cartridges.</para>
	      
	  <para>Data transfer rate is XXX</para>
	  
	  <para>This drive can read and write DC2300 (550MB), DC2750 (750MB),
	    MC3000 (750MB), and MC3000XL (1GB) mini cartridges.</para>
	      
	  <para>WARNING: This drive does not meet the SCSI-2 specifications.
	    The drive locks up completely in response to a SCSI MODE_SELECT
	    command unless there is a formatted tape in the drive.  Before
	    using this drive, set the tape blocksize with</para>
	      
	  <screen>&prompt.root; <userinput>mt -f /dev/st0ctl.0 blocksize 1024</userinput></screen>
	      
	  <para>Before using a mini cartridge for the first time, the
	    mini cartridge must be formated.  FreeBSD 2.1.0-RELEASE and
	    earlier:</para>
	      
	  <screen>&prompt.root; <userinput>/sbin/scsi -f /dev/rst0.ctl -s 600 -c "4 0 0 0 0 0"</userinput></screen>
	      
	  <para>(Alternatively, fetch a copy of the
	    <command>scsiformat</command> shell script from FreeBSD
	    2.1.5/2.2.) FreeBSD 2.1.5 and later:</para>
	      
	  <screen>&prompt.root; <userinput>/sbin/scsiformat -q -w /dev/rst0.ctl</userinput></screen>
	      
	  <para>Right now, this drive cannot really be recommended for
	    FreeBSD.</para>
	      
	  <para>Reported by: Bob Beaulieu
	    <email>ez@eztravel.com</email></para>
	</sect3>

	<sect3 id="hw-storage-exb8200">
	  <title>Exabyte EXB-8200</title>
	  
	  <para>The boot message identifier for this drive is <literal>EXABYTE
	      EXB-8200 252X</literal> <literal>type 1 removable SCSI
	      1</literal></para>
	      
	  <para>This is an 8mm tape drive.</para>
	  
	  <para>Native capacity is 2.3GB.</para>
	  
	  <para>Data transfer rate is 270kB/s.</para>
	  
	  <para>This drive is fairly slow in responding to the SCSI bus during
	    boot.  A custom kernel may be required (set SCSI_DELAY to 10
	    seconds).</para>
	  
	  <para>There are a large number of firmware configurations for this
	    drive, some have been customized to a particular vendor's
	    hardware.  The firmware can be changed via EPROM
	    replacement.</para>
	      
	  <para>Production of this drive has been discontinued.</para>
	  
	  <para>Reported by: &a.msmith;</para>
	</sect3>

	<sect3 id="hw-storage-exb8500">
	  <title>Exabyte EXB-8500</title>
	  
	  <para>The boot message identifier for this drive is <literal>EXABYTE
	      EXB-8500-85Qanx0 0415</literal> <literal>type 1 removable SCSI
	      2</literal></para>
	      
	  <para>This is an 8mm tape drive.</para>
	  
	  <para>Native capacity is 5GB.</para>
	  
	  <para>Data transfer rate is 300kB/s.</para>
	      
	  <para>Reported by: Greg Lehey <email>grog@lemis.de</email></para>
	</sect3>

	<sect3 id="hw-storage-exb8505">
	  <title><ulink
	      url="http://www.Exabyte.COM:80/Products/8mm/8505XL/Rfeatures.html">Exabyte EXB-8505</ulink></title>
	      
	      <para>The boot message identifier for this drive is
	    <literal>EXABYTE EXB-85058SQANXR1 05B0</literal> <literal>type 1
	      removable SCSI 2</literal></para>
	      
	  <para>This is an 8mm tape drive which supports compression, and is
	    upward compatible with the EXB-5200 and EXB-8500.</para>
	  
	  <para>Native capacity is 5GB.</para>
	  
	  <para>The drive supports hardware data compression.</para>
	  
	  <para>Data transfer rate is 300kB/s.</para>
	  
	  <para>Reported by: Glen Foster
	    <email>gfoster@gfoster.com</email></para>
	</sect3>

	<sect3 id="hw-storage-hp1533a">
	  <title>Hewlett-Packard HP C1533A</title>
	  
	  <para>The boot message identifier for this drive is <literal>HP
	      C1533A 9503</literal> <literal>type 1 removable SCSI
	      2</literal>.</para>
	      
	  <para>This is a DDS-2 tape drive.  DDS-2 means hardware data
	    compression and narrower tracks for increased data
	    capacity.</para>
	  
	  <para>Native capacity is 4GB when using 120m tapes.  This drive
	    supports hardware data compression.</para>
	      
	  <para>Data transfer rate is 510kB/s.</para>
	  
	  <para>This drive is used in Hewlett-Packard's SureStore 6000eU and
	    6000i tape drives and C1533A DDS-2 DAT drive.</para>
	  
	  <para>The drive has a block of 8 dip switches.  The proper settings
	    for FreeBSD are: 1 ON; 2 ON; 3 OFF; 4 ON; 5 ON; 6 ON; 7 ON; 8
	    ON.</para>
	  
	  <informaltable frame="none">
	    <tgroup cols="3">
	      <thead>
		<row>
		  <entry>switch 1</entry>
		  <entry>switch 2</entry>
		  <entry>Result</entry>
		</row>
	      </thead>
	      
	      <tbody>
		<row>
		  <entry>On</entry>
		  <entry>On</entry>
		  <entry>Compression enabled at power-on, with host
		    control</entry>
		</row>
		
		<row>
		  <entry>On</entry>
		  <entry>Off</entry>
		  <entry>Compression enabled at power-on, no host
		    control</entry>
		</row>
		
		<row>
		  <entry>Off</entry>
		  <entry>On</entry>
		  <entry>Compression disabled at power-on, with host
		    control</entry>
		</row>
		
		<row>
		  <entry>Off</entry>
		  <entry>Off</entry>
		  <entry>Compression disabled at power-on, no host
		    control</entry>
		</row>
	      </tbody>
	    </tgroup>
	  </informaltable>
	  
	  <para>Switch 3 controls MRS (Media Recognition System).  MRS tapes
	    have stripes on the transparent leader.  These identify the tape
	    as DDS (Digital Data Storage) grade media.  Tapes that do not have
	    the stripes will be treated as write-protected.  Switch 3 OFF
	    enables MRS.  Switch 3 ON disables MRS.</para>
	      
	      <para>See <ulink url="http://www.hp.com/tape/c_intro.html">HP
	      SureStore Tape Products</ulink> and <ulink
	      url="http://www.impediment.com/hp/hp_technical.html">Hewlett-Packard
	      Disk and Tape Technical Information</ulink> for more information
	    on configuring this drive.</para>
	      
	  <para><emphasis>Warning:</emphasis> Quality control on these drives
	    varies greatly.  One FreeBSD core-team member has returned 2 of
	    these drives.  Neither lasted more than 5 months.</para>
	      
	  <para>Reported by: &a.se;</para>
	</sect3>

	<sect3 id="hw-storage-hp1534a">
	  <title>Hewlett-Packard HP 1534A</title>
	  
	  <para>The boot message identifier for this drive is <literal>HP
	      HP35470A T503</literal> <literal>type 1 removable SCSI
	      2</literal> <literal>Sequential-Access density code 0x13,
	      variable blocks</literal>.</para>
	      
	  <para>This is a DDS-1 tape drive.  DDS-1 is the original DAT tape
	    format.</para>
	      
	  <para>Native capacity is 2GB when using 90m tapes.</para>
	      
	  <para>Data transfer rate is 183kB/s.</para>
	  
	  <para>The same mechanism is used in Hewlett-Packard's SureStore
	    <ulink url="http://www.dmo.hp.com/tape/sst2000.htm">2000i</ulink>
	    tape drive, C35470A DDS format DAT drive, C1534A DDS format DAT
	    drive and HP C1536A DDS format DAT drive.</para>
	      
	  <para>The HP C1534A DDS format DAT drive has two indicator lights,
	    one green and one amber.  The green one indicates tape action:
	    slow flash during load, steady when loaded, fast flash during
	    read/write operations.  The amber one indicates warnings: slow
	    flash when cleaning is required or tape is nearing the end of its
	    useful life, steady indicates an hard fault.  (factory service
	    required?)</para>
	      
	  <para>Reported by Gary Crutcher
	    <email>gcrutchr@nightflight.com</email></para>
	</sect3>

	<sect3 id="hw-storage-hp1553a">
	  <title>Hewlett-Packard HP C1553A Autoloading DDS2</title>
	  
	  <para>The boot message identifier for this drive is "".</para>
	  
	  <para>This is a DDS-2 tape drive with a tape changer.  DDS-2 means
	    hardware data compression and narrower tracks for increased data
	    capacity.</para>
	      
	  <para>Native capacity is 24GB when using 120m tapes.  This drive
	    supports hardware data compression.</para>
	      
	  <para>Data transfer rate is 510kB/s (native).</para>
	      
	  <para>This drive is used in Hewlett-Packard's SureStore <ulink
	      url="http://www.dmo.hp.com/tape/sst12000.htm">12000e</ulink>
	    tape drive.</para>
	      
	  <para>The drive has two selectors on the rear panel.  The selector
	    closer to the fan is SCSI id.  The other selector should be set to
	    7.</para>
	      
	  <para>There are four internal switches.  These should be set: 1 ON;
	    2 ON; 3 ON; 4 OFF.</para>
	      
	  <para>At present the kernel drivers do not automatically change
	    tapes at the end of a volume.  This shell script can be used to
	    change tapes:</para>
	      
	  <programlisting>#!/bin/sh
PATH="/sbin:/usr/sbin:/bin:/usr/bin"; export PATH

usage()
{
        echo "Usage: dds_changer [123456ne] raw-device-name
        echo "1..6 = Select cartridge"
        echo "next cartridge"
        echo "eject magazine"
        exit 2
}

if [ $# -ne 2 ] ; then
        usage
fi

cdb3=0
cdb4=0
cdb5=0

case $1 in
        [123456])
                cdb3=$1
                cdb4=1
                ;;
        n)
                ;;
        e)
                cdb5=0x80
                ;;
        ?)
                usage
                ;;
esac

scsi -f $2 -s 100 -c "1b 0 0 $cdb3 $cdb4 $cdb5"</programlisting>
	</sect3>

	<sect3 id="hw-storage-hp35450a">
	  <title>Hewlett-Packard HP 35450A</title>
	  
	  <para>The boot message identifier for this drive is <literal>HP
	      HP35450A -A C620</literal> <literal>type 1 removable SCSI
	      2</literal> <literal>Sequential-Access density code
	      0x13</literal></para>
	      
	  <para>This is a DDS-1 tape drive.  DDS-1 is the original DAT tape
	    format.</para>
	      
	  <para>Native capacity is 1.2GB.</para>
	      
	  <para>Data transfer rate is 160kB/s.</para>
	  
	  <para>Reported by: Mark Thompson
	    <email>mark.a.thompson@pobox.com</email></para>
	</sect3>

	<sect3 id="hw-storage-hp35470a">
	  <title>Hewlett-Packard HP 35470A</title>
	  
	  <para>The boot message identifier for this drive is <literal>HP
	      HP35470A 9 09</literal> <literal>type 1 removable SCSI
	      2</literal></para>
	      
	  <para>This is a DDS-1 tape drive.  DDS-1 is the original DAT tape
	    format.</para>
	      
	  <para>Native capacity is 2GB when using 90m tapes.</para>
	      
	  <para>Data transfer rate is 183kB/s.</para>
	  
	  <para>The same mechanism is used in Hewlett-Packard's SureStore
	    <ulink url="http://www.dmo.hp.com/tape/sst2000.htm">2000i</ulink>
	    tape drive, C35470A DDS format DAT drive, C1534A DDS format DAT
	    drive, and HP C1536A DDS format DAT drive.</para>
	      
	  <para><emphasis>Warning:</emphasis> Quality control on these drives
	    varies greatly.  One FreeBSD core-team member has returned 5 of
	    these drives.  None lasted more than 9 months.</para>
	      
	  <para>Reported by: David Dawes
	    <email>dawes@rf900.physics.usyd.edu.au</email> (9 09)</para>
	      
	</sect3>

	<sect3 id="hw-storage-hp35480a">
	  <title>Hewlett-Packard HP 35480A</title>
	  
	  <para>The boot message identifier for this drive is <literal>HP
	      HP35480A 1009</literal> <literal>type 1 removable SCSI
	      2</literal> <literal>Sequential-Access density code
	      0x13</literal>.</para>
	      
	  <para>This is a DDS-DC tape drive.  DDS-DC is DDS-1 with hardware
	    data compression.  DDS-1 is the original DAT tape format.</para>
	      
	  <para>Native capacity is 2GB when using 90m tapes.  It cannot handle
	    120m tapes.  This drive supports hardware data compression.
	    Please refer to the section on <link
	      linkend="hw-storage-hp1533a">HP C1533A</link> for the proper
	    switch settings.</para>
	      
	  <para>Data transfer rate is 183kB/s.</para>
	  
	  <para>This drive is used in Hewlett-Packard's SureStore <ulink
	      url="http://www.dmo.hp.com/tape/sst5000.htm">5000eU</ulink> and
	    <ulink url="http://www.dmo.hp.com/tape/sst5000.htm">5000i</ulink>
	    tape drives and C35480A DDS format DAT drive..</para>
	      
	  <para>This drive will occasionally hang during a tape eject
	    operation (<command>mt offline</command>). Pressing the front
	    panel button will eject the tape and bring the tape drive back to
	    life.</para>
	      
	  <para>WARNING: HP 35480-03110 only.  On at least two occasions this
	    tape drive when used with FreeBSD 2.1.0, an IBM Server 320 and an
	    2940W SCSI controller resulted in all SCSI disk partitions being
	    lost.  The problem has not be analyzed or resolved at this
	    time.</para>
	</sect3>

	<sect3 id="hw-storage-sdt5000">
	  <title><ulink
	      url="http://www.sel.sony.com/SEL/ccpg/storage/tape/t5000.html">Sony SDT-5000</ulink></title>
	      
	  <para>There are at least two significantly different models: one is
	    a DDS-1 and the other DDS-2.  The DDS-1 version is
	    <literal>SDT-5000 3.02</literal>.  The DDS-2 version is
	    <literal>SONY SDT-5000 327M</literal>. The DDS-2 version has a 1MB
	    cache.  This cache is able to keep the tape streaming in almost
	    any circumstances.</para>
	      
	  <para>The boot message identifier for this drive is <literal>SONY
	      SDT-5000 3.02</literal> <literal>type 1 removable SCSI
	      2</literal> <literal>Sequential-Access density code
	      0x13</literal></para>
	      
	  <para>Native capacity is 4GB when using 120m tapes.  This drive
	    supports hardware data compression.</para>
	      
	  <para>Data transfer rate is depends upon the model or the drive. The
	    rate is 630kB/s for the <literal>SONY SDT-5000 327M</literal>
	    while compressing the data.  For the <literal>SONY SDT-5000
	      3.02</literal>, the data transfer rate is 225kB/s.</para>
	      
	  <para>In order to get this drive to stream, set the blocksize to 512
	    bytes (<command>mt blocksize 512</command>) reported by Kenneth
	    Merry <email>ken@ulc199.residence.gatech.edu</email>.</para>
	      
	  <para><literal>SONY SDT-5000 327M</literal> information reported by
	    Charles Henrich <email>henrich@msu.edu</email>.</para>
	      
	  <para>Reported by: &a.jmz;</para>
	</sect3>

	<sect3 id="hw-storage-tandberg3600">
	  <title>Tandberg TDC 3600</title>
	  
	  <para>The boot message identifier for this drive is
	    <literal>TANDBERG TDC 3600 =08:</literal> <literal>type 1
	      removable SCSI 2</literal></para>
	      
	  <para>This is a QIC tape drive.</para>
	  
	  <para>Native capacity is 150/250MB.</para>
	  
	  <para>This drive has quirks which are known and work around code is
	    present in the scsi tape device driver (&man.st.4;).
	    Upgrading the firmware to XXX version will fix the quirks and
	    provide SCSI 2 capabilities.</para>
	      
	  <para>Data transfer rate is 80kB/s.</para>
	  
	  <para>IBM and Emerald units will not work.  Replacing the firmware
	    EPROM of these units will solve the problem.</para>
	      
	  <para>Reported by: &a.msmith;</para>
	</sect3>

	<sect3 id="hw-storage-tandberg3620">
	  <title>Tandberg TDC 3620</title>
	  
	  <para>This is very similar to the <link
	      linkend="hw-storage-tandberg3600">Tandberg TDC 3600</link>
	    drive.</para>
	      
	  <para>Reported by: &a.joerg;</para>
	</sect3>

	<sect3 id="hw-storage-tandberg3800">
	  <title>Tandberg TDC 3800</title>

	  <para>The boot message identifier for this drive is
	    <literal>TANDBERG TDC 3800 =04Y</literal> <literal>Removable
	      Sequential Access SCSI-2 device</literal></para>
	      
	  <para>This is a QIC tape drive.</para>
	  
	  <para>Native capacity is 525MB.</para>
	  
	  <para>Reported by: &a.jhs;</para>
	</sect3>

	<sect3 id="hw-storage-tandberg4222">
	  <title>Tandberg TDC 4222</title>
	  
	  <para>The boot message identifier for this drive is
	    <literal>TANDBERG TDC 4222 =07</literal> <literal>type 1 removable
	      SCSI 2</literal></para>
	      
	  <para>This is a QIC tape drive.</para>
	  
	  <para>Native capacity is 2.5GB.  The drive will read all cartridges
	    from the 60 MB (DC600A) upwards, and write 150 MB (DC6150)
	    upwards.  Hardware compression is optionally supported for the 2.5
	    GB cartridges.</para>
	      
	  <para>This drives quirks are known and pre-compiled into the scsi
	    tape device driver (&man.st.4;) beginning with FreeBSD
	    2.2-CURRENT.  For previous versions of FreeBSD, use
	    <command>mt</command> to read one block from the tape, rewind the
	    tape, and then execute the backup program (<command>mt fsr 1; mt
	      rewind; dump ...</command>)</para>
	      
	  <para>Data transfer rate is 600kB/s (vendor claim with compression),
	    350 KB/s can even be reached in start/stop mode. The rate
	    decreases for smaller cartridges.</para>
	  
	  <para>Reported by: &a.joerg;</para>
	</sect3>

	<sect3 id="hw-storage-wangtek5525es">
	  <title>Wangtek 5525ES</title>
	  
	  <para>The boot message identifier for this drive is <literal>WANGTEK
	      5525ES SCSI REV7 3R1</literal> <literal>type 1 removable SCSI
	      1</literal> <literal>density code 0x11, 1024-byte
	      blocks</literal></para>
	      
	  <para>This is a QIC tape drive.</para>
	  
	  <para>Native capacity is 525MB.</para>
	  
	  <para>Data transfer rate is 180kB/s.</para>
	  
	  <para>The drive reads 60, 120, 150, and 525MB tapes.  The drive will
	    not write 60MB (DC600 cartridge) tapes.  In order to overwrite 120
	    and 150 tapes reliably, first erase (<command>mt erase</command>)
	    the tape.  120 and 150 tapes used a wider track (fewer tracks per
	    tape) than 525MB tapes. The <quote>extra</quote> width of the
	    previous tracks is not overwritten, as a result the new data lies
	    in a band surrounded on both sides by the previous data unless the
	    tape have been erased.</para>
	      
	  <para>This drives quirks are known and pre-compiled into the scsi
	    tape device driver (&man.st.4;).</para>
	  
	  <para>Other firmware revisions that are known to work are:
	    M75D</para>
	  
	  <para>Reported by: Marc van Kempen <email>marc@bowtie.nl</email>
	    <literal>REV73R1</literal> Andrew Gordon
	    <email>Andrew.Gordon@net-tel.co.uk</email>
	    <literal>M75D</literal></para>
	</sect3>

	<sect3 id="hw-storage-wangtek6200">
	  <title>Wangtek 6200</title>
	  
	  <para>The boot message identifier for this drive is <literal>WANGTEK
	      6200-HS 4B18</literal> <literal>type 1 removable SCSI
	      2</literal> <literal>Sequential-Access density code
	      0x13</literal></para>
	  
	  <para>This is a DDS-1 tape drive.</para>
	  
	  <para>Native capacity is 2GB using 90m tapes.</para>
	  
	  <para>Data transfer rate is 150kB/s.</para>
	  
	  <para>Reported by: Tony Kimball <email>alk@Think.COM</email></para>
	</sect3>
      </sect2>
      
      <sect2>
	<title>* Problem drives</title>

	<para></para>
      </sect2>
    </sect1>
    
    <sect1>
      <title>CDROM drives</title>
      
      <para><emphasis>Contributed by &a.obrien;.  23 November
	      1997.</emphasis></para>
      
      <para>Generally speaking those in <emphasis>The FreeBSD
	Project</emphasis> prefer SCSI CDROM drives over IDE CDROM
	drives.  However not all SCSI CDROM drives are equal.  Some
	feel the quality of some SCSI CDROM drives have been
	deteriorating to that of IDE CDROM drives.  Toshiba used to be
	the favored stand-by, but many on the SCSI mailing list have
	found displeasure with the 12x speed XM-5701TA as its volume
	(when playing audio CDROMs) is not controllable by the various
	audio player software.</para>
	  
      <para>Another area where SCSI CDROM manufacturers are cutting corners is
	adherence to the <link linkend="scsi-further-reading">SCSI
	  specification</link>. Many SCSI CDROMs will respond to <link
	  linkend="scsi-rogue-devices">multiple LUNs</link> for its target
	address.  Known violators include the 6x Teac CD-56S 1.0D.</para>
  </sect1>

</article>
