New section about SCSI hard drives. Not that I'm an expert or anything,

but it was embarrassing to leave that entry empty!

handbook/Makefile

@@ -1,4 +1,4 @@
-# $Id: Makefile,v 1.28 1997-11-18 16:06:04 wosch Exp $
+# $Id: Makefile,v 1.29 1998-02-19 06:45:26 asami Exp $
 
 SGMLOPTS=-links
 SRCS= authors.sgml basics.sgml bibliography.sgml boothelp.sgml
@@ -12,7 +12,8 @@ SRCS+= lists.sgml mail.sgml memoryuse.sgml
 SRCS+= mirrors.sgml nfs.sgml nutshell.sgml pgpkeys.sgml policies.sgml
 SRCS+= porting.sgml ports.sgml ppp.sgml printing.sgml 
 SRCS+= quotas.sgml relnotes.sgml routing.sgml russian.sgml
-SRCS+= serial.sgml scsi.sgml sections.sgml sio.sgml skey.sgml slipc.sgml 
+SRCS+= serial.sgml scsi.sgml scsihd.sgml
+SRCS+= sections.sgml sio.sgml skey.sgml slipc.sgml 
 SRCS+= slips.sgml stable.sgml submitters.sgml synching.sgml 
 SRCS+= term.sgml userppp.sgml uart.sgml linuxemu.sgml
 

handbook/hw.sgml

@@ -1,4 +1,4 @@
-<!-- $Id: hw.sgml,v 1.78 1997-12-29 16:34:30 asami Exp $ -->
+<!-- $Id: hw.sgml,v 1.79 1998-02-19 06:45:27 asami Exp $ -->
 <!-- The FreeBSD Documentation Project -->
 
 <!--
@@ -451,7 +451,11 @@ Slippery when wet.  Beware of dog.
   <sect2><heading>* IDE</heading>
   <sect2><heading>* Floppy</heading>
 
-<sect1><heading>* Hard drives</heading>
+<sect1><heading> Hard drives</heading>
+&scsihd;
+
+  <sect2><heading>* IDE hard drives</heading>
+
 <sect1><heading> Tape drives</heading>
 	  <p><em>Contributed by &a.jmb;.<newline>2 July 1996.</em></p>
   <sect2><heading> General tape access commands</heading>

handbook/scsihd.sgml

@@ -0,0 +1,123 @@
+<!-- $Id -->
+<!-- The FreeBSD Documentation Project -->
+
+<!--
+<!DOCTYPE chapt PUBLIC "-//FreeBSD//DTD linuxdoc//EN"> -->
+
+  <sect2><heading> SCSI hard drives</heading>
+  <p><em>Contributed by &a.asami;.<newline>17 February 1998.</em></p>
+
+      <p>As mentioned in the <ref id="scsi" name="SCSI"> 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 <ref id="scsi" name="SCSI">
+	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.
+
+    <sect3><heading> Rotational speed</heading>
+      <p>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.
+
+      <p>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 "internal data (or transfer) rate".  It is
+	usually in megabits/sec so divide it by 8 and you'll get the
+	rough approximation of how much megabytes/sec you can get out
+	of the drive.
+
+      <p>(If you are a speed maniac and want a 10,000RPM drive for
+	your cute little peecee, be my guest; however, those drives
+	become extremely hot.  Don't even think about it if you don't
+	have a fan blowing air <em>directly at</em> the drive or a
+	properly ventilated disk enclosure.)
+
+      <p>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's 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.
+
+      <p>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" (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.
+
+      <p>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.
+
+    <sect3><heading> Form factor</heading>
+      <p>Most SCSI drives sold today are of 3.5" form factor.  They
+	come in two different heights; 1.6" ("half-height") or 1"
+	("low-profile"). The half-height drive is the same height as a
+	CD-ROM drive.  However, don't forget the spacing rule
+	mentioned in the previous section.  If you have three standard
+	3.5" drive bays, you will not be able to put three half-height
+	drives in there (without frying them, that is).
+
+    <sect3><heading> Interface</heading>
+      <p>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.
+
+      <p>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's much easier to get it "right".  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't afford the cost
+	difference, you shouldn't be building a disk array.)
+
+      <p>There are two variant of wide SCSI drives; 68-pin and 80-pin
+	SCA (Single Connector Attach).  The SCA drives don't 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 "stub" 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).

handbook/sections.sgml

@@ -1,4 +1,4 @@
-<!-- $Id: sections.sgml,v 1.26 1997-11-18 16:06:09 wosch Exp $ -->
+<!-- $Id: sections.sgml,v 1.27 1998-02-19 06:45:30 asami Exp $ -->
 <!-- The FreeBSD Documentation Project -->
 
 <!-- Entities containing all the pieces of the handbook are -->
@@ -51,6 +51,7 @@
 <!ENTITY russian SYSTEM "russian.sgml">
 <!ENTITY serial SYSTEM "serial.sgml">
 <!ENTITY scsi SYSTEM "scsi.sgml">
+<!ENTITY scsihd SYSTEM "scsihd.sgml">
 <!ENTITY sio SYSTEM "sio.sgml">
 <!ENTITY cy SYSTEM "cyclades.sgml">
 <!ENTITY skey SYSTEM "skey.sgml">