From d7a17bf2f2e9d965b9122f46ad106e5a688ce694 Mon Sep 17 00:00:00 2001
From: Chern Lee <chern@FreeBSD.org>
Date: Wed, 12 Sep 2001 23:55:00 +0000
Subject: [PATCH] Moved Disk Naming and BIOS Drive Numbering sections from
Storage chapter into Install chapter as "Installation Destination"
Suggested by: murray and nik
---
.../books/handbook/install/chapter.sgml | 236 +++++++++++++++++-
1 file changed, 235 insertions(+), 1 deletion(-)
diff --git a/en_US.ISO8859-1/books/handbook/install/chapter.sgml b/en_US.ISO8859-1/books/handbook/install/chapter.sgml
index 0e7b098693..58eb4f0503 100644
--- a/en_US.ISO8859-1/books/handbook/install/chapter.sgml
+++ b/en_US.ISO8859-1/books/handbook/install/chapter.sgml
@@ -1,7 +1,7 @@
<!--
The FreeBSD Documentation Project
- $FreeBSD: doc/en_US.ISO8859-1/books/handbook/install/chapter.sgml,v 1.113 2001/09/11 01:11:01 murray Exp $
+ $FreeBSD: doc/en_US.ISO8859-1/books/handbook/install/chapter.sgml,v 1.114 2001/09/11 18:48:03 chern Exp $
-->
<chapter id="install">
@@ -1212,6 +1212,240 @@ Mounting root from ufs:/dev/md0c
</sect2>
</sect1>
+ <sect1 id="install-drive">
+ <title>Installation Destination</title>
+
+ <sect2 id="disks-naming">
+ <title>Disk Naming</title>
+
+ <indexterm><primary>IDE</primary></indexterm>
+ <indexterm><primary>SCSI</primary></indexterm>
+ <indexterm><primary>RAID</primary></indexterm>
+ <indexterm><primary>flash memory</primary></indexterm>
+ <para>Physical drives come in two main flavors,
+ <acronym>IDE</acronym>, or <acronym>SCSI</acronym>; but there
+ are also drives backed by RAID controllers, flash memory, and so
+ forth. Since these behave quite differently, they have their
+ own drivers and devices.</para>
+
+ <table id="disk-naming-physical-table">
+ <title>Physical Disk Naming Conventions</title>
+
+ <tgroup cols="2">
+ <thead>
+ <row>
+ <entry>Drive type</entry>
+ <entry>Drive device name</entry>
+ </row>
+ </thead>
+ <tbody>
+ <row>
+ <entry>IDE hard drives</entry>
+ <entry><literal>ad</literal> in 4.0-RELEASE,
+ <literal>wd</literal> before 4.0-RELEASE.</entry>
+ </row>
+ <row>
+ <entry>IDE CDROM drives</entry>
+ <entry><literal>acd</literal> from 4.0-RELEASE,
+ <literal>wcd</literal> before 4.0-RELEASE.</entry>
+ </row>
+ <row>
+ <entry>SCSI hard drives and USB Mass storage devices</entry>
+ <entry><literal>da</literal> from 3.0-RELEASE,
+ <literal>sd</literal> before 3.0-RELEASE.</entry>
+ </row>
+ <row>
+ <entry>SCSI CDROM drives</entry>
+ <entry><literal>cd</literal></entry>
+ </row>
+ <row>
+ <entry>Assorted non-standard CDROM drives</entry>
+ <entry><literal>mcd</literal> for Mitsumi CD-ROM,
+ <literal>scd</literal> for Sony CD-ROM,
+ <literal>matcd</literal> for Matsushita/Panasonic CD-ROM
+ </entry>
+ </row>
+ <row>
+ <entry>Floppy drives</entry>
+ <entry><literal>fd</literal></entry>
+ </row>
+ <row>
+ <entry>SCSI tape drives</entry>
+ <entry><literal>sa</literal> from 3.0-RELEASE,
+ <literal>st</literal> before 3.0-RELEASE.</entry>
+ </row>
+ <row>
+ <entry>IDE tape drives</entry>
+ <entry><literal>ast</literal> from 4.0-RELEASE,
+ <literal>wst</literal> before 4.0-RELEASE.</entry>
+ </row>
+ <row>
+ <entry>Flash drives</entry>
+ <entry><literal>fla</literal> for DiskOnChip Flash device
+ from 3.3-RELEASE.</entry>
+ </row>
+ <row>
+ <entry>RAID drives</entry>
+ <entry><literal>myxd</literal> for Mylex, and
+ <literal>amrd</literal> for AMI MegaRAID,
+ <literal>idad</literal> for Compaq Smart RAID.
+ from 4.0-RELEASE. <literal>id</literal> between
+ 3.2-RELEASE and 4.0-RELEASE.</entry>
+ </row>
+ </tbody>
+ </tgroup>
+ </table>
+
+ <para>All the drives attached through a specific driver are
+ numbered starting at 0. So the first IDE drive would be
+ <quote>ad<emphasis>0</emphasis></quote>. You seldom need to use
+ these devices.</para>
+
+ <sect3 id="slicesandpartitions">
+ <title>Slices and Partitions</title>
+ <indexterm><primary>slices</primary></indexterm>
+ <indexterm><primary>partitions</primary></indexterm>
+ <indexterm><primary>dangerously dedicated</primary></indexterm>
+ <para>Physical disks usually contain
+ <firstterm>slices</firstterm>, unless they are
+ <quote>dangerously dedicated</quote>. Slice numbers follow
+ the device name, prefixed with an <literal>s</literal>,
+ starting at 1. So <quote>da0<emphasis>s1</emphasis></quote>
+ is the first slice on the first SCSI drive. There can only be
+ four physical slices on a disk, but you can have logical
+ slices inside physical slices of the appropriate type. These
+ extended slices are numbered starting at 5, so
+ <quote>ad0<emphasis>s5</emphasis></quote> is the first
+ extended slice on a disk. These devices are used by file
+ systems that expect to occupy a slice.</para>
+
+ <para>Slices, <quote>dangerously dedicated</quote> physical
+ drives, and other drives contain
+ <firstterm>partitions</firstterm>, which are represented as
+ letters from <literal>a</literal> to <literal>h</literal>.
+ This letter is appended to the device name, so
+ <quote>da0<emphasis>a</emphasis></quote> is the a partition on
+ the first da drive, which is <quote>dangerously dedicated</quote>.
+ <quote>ad1s3<emphasis>e</emphasis></quote> is the fifth partition
+ in the third slice of the second IDE disk drive.</para>
+
+ <para>The boot code expects partition <literal>a</literal> to be
+ the root partition. Partition <literal>b</literal> is normally
+ reserved for swap partitions, and <literal>c</literal> is an
+ unused partition the size of the entire slice or drive. This
+ is explained in <xref linkend="disks-adding">.</para>
+ </sect3>
+ </sect2>
+
+ <sect2 id="install-drive-bios-numbering">
+ <title>BIOS Drive Numbering</title>
+
+ <para>Before you install and configure FreeBSD on your system, there is an
+ important subject that you should be aware of, especially if you have
+ multiple hard drives.</para>
+
+ <indexterm><primary>DOS</primary></indexterm>
+ <indexterm><primary>Microsoft Windows</primary></indexterm>
+ <para>In a PC running a BIOS-dependent operating system such as
+ MS-DOS or Microsoft Windows, the BIOS is able to abstract the
+ normal disk drive order, and
+ the operating system goes along with the change. This allows the user
+ to boot from a disk drive other than the so-called <quote>primary
+ master</quote>. This is especially convenient for some users who have
+ found that the simplest and cheapest way to keep a system backup is to
+ buy an identical second hard drive, and perform routine copies of the
+ first drive to the second drive using
+ <application>Ghost</application> or <application>XCOPY</application>
+ . Then, if the
+ first drive fails, or is attacked by a virus, or is scribbled upon by an
+ operating system defect, he can easily recover by instructing the BIOS
+ to logically swap the drives. It is like switching the cables on the
+ drives, but without having to open the case.</para>
+
+ <indexterm><primary>SCSI</primary></indexterm>
+ <indexterm><primary>BIOS</primary></indexterm>
+ <para>More expensive systems with SCSI controllers often include BIOS
+ extensions which allow the SCSI drives to be re-ordered in a similar
+ fashion for up to seven drives.</para>
+
+ <para>A user who is accustomed to taking advantage of these features may
+ become surprised when the results with FreeBSD are not as expected.
+ FreeBSD does not use the BIOS, and does not know the <quote>logical BIOS
+ drive mapping</quote>. This can lead to very perplexing situations,
+ especially when drives are physically identical in geometry, and have
+ also been made as data clones of one another.</para>
+
+ <para>When using FreeBSD, always restore the BIOS to natural drive
+ numbering before installing FreeBSD, and then leave it that way. If you
+ need to switch drives around, then do so, but do it the hard way, and
+ open the case and move the jumpers and cables.</para>
+
+ <sidebar>
+ <title>An Illustration from the Files of Bill and Fred's Exceptional
+ Adventures:</title>
+
+ <para>Bill breaks-down an older Wintel box to make another FreeBSD box
+ for Fred. Bill installs a single SCSI drive as SCSI unit zero and
+ installs FreeBSD on it.</para>
+
+ <para>Fred begins using the system, but after several days notices that
+ the older SCSI drive is reporting numerous soft errors and reports
+ this fact to Bill.</para>
+
+ <para>After several more days, Bill decides it is time to address the
+ situation, so he grabs an identical SCSI drive from the disk drive
+ <quote>archive</quote> in the back room. An initial surface scan
+ indicates that
+ this drive is functioning well, so Bill installs this drive as SCSI
+ unit four and makes an image copy from drive zero to drive four. Now
+ that the new drive is installed and functioning nicely, Bill decides
+ that it is a good idea to start using it, so he uses features in the
+ SCSI BIOS to re-order the disk drives so that the system boots from
+ SCSI unit four. FreeBSD boots and runs just fine.</para>
+
+ <para>Fred continues his work for several days, and soon Bill and Fred
+ decide that it is time for a new adventure -- time to upgrade to a
+ newer version of FreeBSD. Bill removes SCSI unit zero because it was
+ a bit flaky and replaces it with another identical disk drive from
+ the <quote>archive.</quote> Bill then installs the new version of FreeBSD onto the
+ new SCSI unit zero using Fred's magic Internet FTP floppies. The
+ installation goes well.</para>
+
+ <para>Fred uses the new version of FreeBSD for a few days, and certifies
+ that it is good enough for use in the engineering department...it is
+ time to copy all of his work from the old version. So Fred mounts
+ SCSI unit four (the latest copy of the older FreeBSD version). Fred
+ is dismayed to find that none of his precious work is present on SCSI
+ unit four.</para>
+
+ <para>Where did the data go?</para>
+
+ <para>When Bill made an image copy of the original SCSI unit zero onto
+ SCSI unit four, unit four became the <quote>new clone,</quote>
+ When Bill
+ re-ordered the SCSI BIOS so that he could boot from SCSI unit four, he
+ was only fooling himself. FreeBSD was still running on SCSI unit zero.
+ Making this kind of BIOS change will cause some or all of the Boot and
+ Loader code to be fetched from the selected BIOS drive, but when the
+ FreeBSD kernel drivers take-over, the BIOS drive numbering will be
+ ignored, and FreeBSD will transition back to normal drive numbering.
+ In the illustration at hand, the system continued to operate on the
+ original SCSI unit zero, and all of Fred's data was there, not on SCSI
+ unit four. The fact that the system appeared to be running on SCSI
+ unit four was simply an artifact of human expectations.</para>
+
+ <para>We are delighted to mention that no data bytes were killed or
+ harmed in any way by our discovery of this phenomenon. The older SCSI
+ unit zero was retrieved from the bone pile, and all of Fred's work was
+ returned to him, (and now Bill knows that he can count as high as
+ zero).</para>
+
+ <para>Although SCSI drives were used in this illustration, the concepts
+ apply equally to IDE drives.</para>
+ </sidebar>
+ </sect2>
+ </sect1>
+
<sect1 id="install-steps">
<title>Allocating Disk Space</title>