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Update scsi.sgml to reflect recent reality. Change Japanese

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translation to match it.  Refine Japanese translation.  Move around
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Submitted by:	asami, Yoshiaki Uchikawa <yoshiaki@kt.rim.or.jp>
This commit is contained in:
Satoshi Asami 1997-12-28 20:18:24 +00:00
parent 149b884bb8
commit 633e4c52a8
Notes: svn2git 2020-12-08 03:00:23 +00:00 
svn path=/head/; revision=2312
3 changed files with 938 additions and 734 deletions
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130
handbook/scsi.sgml
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@ -1,4 +1,4 @@
<!-- $Id: scsi.sgml,v 1.24 1997-12-25 09:36:38 hoek Exp $ -->
<!-- $Id: scsi.sgml,v 1.25 1997-12-28 20:18:14 asami Exp $ -->
<!-- The FreeBSD Documentation Project -->
<!--
@ -49,9 +49,10 @@
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 mega-transfers per second
(20 Mbytes/sec on a 8 bit bus), Fast-40 is 40 mega-transfers per
second (40 Mbytes/sec on a 8 bit bus).
(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).
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
@ -91,7 +92,7 @@
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
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
@ -160,7 +161,7 @@
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 'slow' SCSI. As discussed before, bus
speeds of 20 and 40 megatransfers/second are also emerging
speeds of 20 and 40 million transfers/second are also emerging
(Fast-20 == Ultra SCSI and Fast-40 == Ultra2 SCSI).
It should be noted that the data lines &gt; 8 are only used for
@ -183,8 +184,8 @@
meters. Fast-SCSI means that instead of 5Mbytes/sec the bus
allows 10Mbytes/sec transfers.
Fast-20 (Ultra SCSI) and Fast-40 allow for 20 and 40
megatransfers/second respectively. So, F20 is 20 Mbytes/second
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
@ -252,7 +253,7 @@
Terminators come in various incarnations, with more or less
sophisticated designs. Of course, there are internal and
external variants. Almost every SCSI device comes with a
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
@ -280,14 +281,15 @@
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: <bf>every SCSI bus has 2 (two)
the simplest. The rule is: <bf>every single line on the SCSI bus has 2 (two)
terminators, one at each end of the bus.</bf> 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.
bugs. (Note the "potential" here; the nastiest part is that
it may or may not work.)
A common pitfall is to have an internal (flat)cable in a
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
@ -295,6 +297,12 @@
general, every reconfiguration of a SCSI bus must pay attention
to this.
Note that 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).
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
@ -305,9 +313,11 @@
used. These things are special purpose integrated circuits that
can be dis/en-abled 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 even are software
configurable, using some sort of setup tool. Consult you
documentation!
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!
<sect3><heading>Terminator power</heading>
<p>
@ -346,11 +356,14 @@
Because the SCSI bus is, ehh, a bus there must be a way to
distinguish or address the different devices connected to it.
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. Consult the documentation of your device for
more information.
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.
Beware of multiple devices configured to use the same ID. Chaos
normally reigns in this case. A pitfall is that one of the
@ -360,13 +373,24 @@
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.
number of data lines (usually 16).
Note that 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
CD-ROM will stop working).
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 (for narrow buses).
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: <tt>[7 6 .. 1 0 15 14 .. 9 8]</tt> on a wide-SCSI
system. (If you you are wondering why the lower 8 have higher
priority, read the previous paragraph for a hint.)
For a further subdivision, the standard allows for Logical
Units or LUNs for short. A single target ID may have multiple
@ -377,12 +401,24 @@
<sect3><heading>Bus layout</heading>
<p>
SCSI buses are linear. So, not shaped like Y-junctions, star
topologies, cobwebs or whatever else people might want to
invent.
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). Don't 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
"Murphy's law").
You might notice that the terminator issue discussed earlier
becomes rather hairy if your bus is not linear.
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.
The electrical characteristics, its noise margins and
ultimately the reliability of it all are tightly related to
@ -433,7 +469,7 @@
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
1 GB. With disk capacities going up all the time this is causing
problems.
Fortunately, the solution is simple: just use another
@ -494,7 +530,7 @@
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)
tape devices (abbreviation: st), magnetic disks (sd), CD-ROMs (cd)
etc. In case you are wondering where you can find this stuff, it
all lives in <tt>/sys/scsi</tt>. See the man pages in section 4
for more details.
@ -519,9 +555,13 @@
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.
the configured hardware was actually found. Note that most
of the EISA/PCI drivers (namely <tt>ahb, ahc, ncr</tt> and
<tt>amd</tt> will automatically obtain the correct parameters
from the host adapters themselves at boot time; thus, you just
need to write, for instance, "<tt>controller ahc0</tt>".
An example loosely based on the FreeBSD 2.0.5-Release kernel config
An example loosely based on the FreeBSD 2.2.5-Release kernel config
file LINT with some added comments (between &lsqb;&rsqb;):
<verb>
@ -532,39 +572,41 @@
# 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!).
#
&lsqb;For an Adaptec AHA274x, 284x etc controller&rsqb;
controller ahc0 at isa? bio irq ? vector ahcintr # port??? iomem?
&lsqb;For an Adaptec AHA274x/284x/294x/394x etc controller&rsqb;
controller ahc0
&lsqb;For an Adaptec AHA174x controller&rsqb;
controller ahb0 at isa? bio irq ? vector ahbintr
&lsqb;For an NCR/Symbios 53c875 based controller&rsqb;
controller ncr0
&lsqb;For an Ultrastor adapter&rsqb;
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 ahb0
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 ahb0]
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]
device cd0 at scbus? [the first ever CD-ROM found, no wiring]
</verb>
The example above tells the kernel to look for a ahc (Adaptec 274x)
controller, then for an Adaptec 174x board, and
controller, then for an NCR/Symbios board, and
so on. The lines following the controller specifications
tell the kernel to configure specific devices but
<em>only</em> attach them when they match the target ID and
@ -616,7 +658,7 @@ device sd0 &lsqb;support for 4 SCSI harddisks, sd0 up sd3&rsqb;
device st0 &lsqb;support for 2 SCSI tapes&rsqb;
&lsqb;for the cdrom&rsqb;
&lsqb;for the CD-ROM&rsqb;
device cd0 #Only need one of these, the code dynamically grows
</verb>
@ -630,14 +672,14 @@ device cd0 #Only need one of these, the code dynamically grows
Use <tt>man 4 scsi</tt> to check for the latest info on the SCSI
subsystem. For more detailed info on host adapter drivers use eg
<tt>man 4 aha</tt> for info on the Adaptec 154x driver.
<tt>man 4 ahc</tt> for info on the Adaptec 294x driver.
<sect3><heading>Tuning your SCSI kernel setup</heading>
<p>
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
kind of device (disk, tape, CD-ROM etc) is connected to a
specific target ID. This process is called device probing by the way.
To work around the 'slow response' problem, FreeBSD allows a
@ -650,7 +692,7 @@ device cd0 #Only need one of these, the code dynamically grows
options SCSI_DELAY=15 #Be pessimistic about Joe SCSI device
</verb>
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.
use 3 seconds minimum to get my trusty old CD-ROM 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.
@ -690,7 +732,7 @@ Mar 29 21:16:37 yedi /kernel: st1: Archive Viper 150 is a known rogue
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
to connect your bogus Mumbletech SCSI CD-ROM you might be the one
that has to define which workaround is needed.
After you got your Mumbletech working, please send the required

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