Moved Disk Naming and BIOS Drive Numbering sections from Storage
chapter into Install chapter as "Installation Destination" Suggested by: murray and nik
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2020-12-08 03:00:23 +00:00
svn path=/head/; revision=10673
1 changed files with 235 additions and 1 deletions
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@ -1,7 +1,7 @@
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<!--
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The FreeBSD Documentation Project
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$FreeBSD: doc/en_US.ISO8859-1/books/handbook/install/chapter.sgml,v 1.113 2001/09/11 01:11:01 murray Exp $
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$FreeBSD: doc/en_US.ISO8859-1/books/handbook/install/chapter.sgml,v 1.114 2001/09/11 18:48:03 chern Exp $
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-->
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<chapter id="install">
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@ -1212,6 +1212,240 @@ Mounting root from ufs:/dev/md0c
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</sect2>
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</sect1>
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<sect1 id="install-drive">
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<title>Installation Destination</title>
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<sect2 id="disks-naming">
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<title>Disk Naming</title>
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<indexterm><primary>IDE</primary></indexterm>
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<indexterm><primary>SCSI</primary></indexterm>
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<indexterm><primary>RAID</primary></indexterm>
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<indexterm><primary>flash memory</primary></indexterm>
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<para>Physical drives come in two main flavors,
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<acronym>IDE</acronym>, or <acronym>SCSI</acronym>; but there
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are also drives backed by RAID controllers, flash memory, and so
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forth. Since these behave quite differently, they have their
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own drivers and devices.</para>
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<table id="disk-naming-physical-table">
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<title>Physical Disk Naming Conventions</title>
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<tgroup cols="2">
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<thead>
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<row>
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<entry>Drive type</entry>
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<entry>Drive device name</entry>
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</row>
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</thead>
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<tbody>
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<row>
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<entry>IDE hard drives</entry>
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<entry><literal>ad</literal> in 4.0-RELEASE,
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<literal>wd</literal> before 4.0-RELEASE.</entry>
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</row>
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<row>
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<entry>IDE CDROM drives</entry>
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<entry><literal>acd</literal> from 4.0-RELEASE,
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<literal>wcd</literal> before 4.0-RELEASE.</entry>
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</row>
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<row>
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<entry>SCSI hard drives and USB Mass storage devices</entry>
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<entry><literal>da</literal> from 3.0-RELEASE,
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<literal>sd</literal> before 3.0-RELEASE.</entry>
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</row>
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<row>
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<entry>SCSI CDROM drives</entry>
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<entry><literal>cd</literal></entry>
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</row>
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<row>
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<entry>Assorted non-standard CDROM drives</entry>
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<entry><literal>mcd</literal> for Mitsumi CD-ROM,
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<literal>scd</literal> for Sony CD-ROM,
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<literal>matcd</literal> for Matsushita/Panasonic CD-ROM
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</entry>
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</row>
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<row>
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<entry>Floppy drives</entry>
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<entry><literal>fd</literal></entry>
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</row>
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<row>
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<entry>SCSI tape drives</entry>
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<entry><literal>sa</literal> from 3.0-RELEASE,
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<literal>st</literal> before 3.0-RELEASE.</entry>
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</row>
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<row>
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<entry>IDE tape drives</entry>
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<entry><literal>ast</literal> from 4.0-RELEASE,
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<literal>wst</literal> before 4.0-RELEASE.</entry>
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</row>
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<row>
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<entry>Flash drives</entry>
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<entry><literal>fla</literal> for DiskOnChip Flash device
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from 3.3-RELEASE.</entry>
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</row>
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<row>
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<entry>RAID drives</entry>
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<entry><literal>myxd</literal> for Mylex, and
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<literal>amrd</literal> for AMI MegaRAID,
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<literal>idad</literal> for Compaq Smart RAID.
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from 4.0-RELEASE. <literal>id</literal> between
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3.2-RELEASE and 4.0-RELEASE.</entry>
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</row>
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</tbody>
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</tgroup>
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</table>
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<para>All the drives attached through a specific driver are
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numbered starting at 0. So the first IDE drive would be
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<quote>ad<emphasis>0</emphasis></quote>. You seldom need to use
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these devices.</para>
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<sect3 id="slicesandpartitions">
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<title>Slices and Partitions</title>
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<indexterm><primary>slices</primary></indexterm>
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<indexterm><primary>partitions</primary></indexterm>
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<indexterm><primary>dangerously dedicated</primary></indexterm>
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<para>Physical disks usually contain
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<firstterm>slices</firstterm>, unless they are
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<quote>dangerously dedicated</quote>. Slice numbers follow
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the device name, prefixed with an <literal>s</literal>,
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starting at 1. So <quote>da0<emphasis>s1</emphasis></quote>
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is the first slice on the first SCSI drive. There can only be
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four physical slices on a disk, but you can have logical
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slices inside physical slices of the appropriate type. These
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extended slices are numbered starting at 5, so
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<quote>ad0<emphasis>s5</emphasis></quote> is the first
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extended slice on a disk. These devices are used by file
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systems that expect to occupy a slice.</para>
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<para>Slices, <quote>dangerously dedicated</quote> physical
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drives, and other drives contain
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<firstterm>partitions</firstterm>, which are represented as
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letters from <literal>a</literal> to <literal>h</literal>.
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This letter is appended to the device name, so
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<quote>da0<emphasis>a</emphasis></quote> is the a partition on
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the first da drive, which is <quote>dangerously dedicated</quote>.
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<quote>ad1s3<emphasis>e</emphasis></quote> is the fifth partition
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in the third slice of the second IDE disk drive.</para>
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<para>The boot code expects partition <literal>a</literal> to be
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the root partition. Partition <literal>b</literal> is normally
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reserved for swap partitions, and <literal>c</literal> is an
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unused partition the size of the entire slice or drive. This
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is explained in <xref linkend="disks-adding">.</para>
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</sect3>
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</sect2>
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<sect2 id="install-drive-bios-numbering">
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<title>BIOS Drive Numbering</title>
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<para>Before you install and configure FreeBSD on your system, there is an
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important subject that you should be aware of, especially if you have
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multiple hard drives.</para>
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<indexterm><primary>DOS</primary></indexterm>
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<indexterm><primary>Microsoft Windows</primary></indexterm>
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<para>In a PC running a BIOS-dependent operating system such as
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MS-DOS or Microsoft Windows, the BIOS is able to abstract the
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normal disk drive order, and
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the operating system goes along with the change. This allows the user
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to boot from a disk drive other than the so-called <quote>primary
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master</quote>. This is especially convenient for some users who have
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found that the simplest and cheapest way to keep a system backup is to
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buy an identical second hard drive, and perform routine copies of the
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first drive to the second drive using
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<application>Ghost</application> or <application>XCOPY</application>
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. Then, if the
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first drive fails, or is attacked by a virus, or is scribbled upon by an
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operating system defect, he can easily recover by instructing the BIOS
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to logically swap the drives. It is like switching the cables on the
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drives, but without having to open the case.</para>
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<indexterm><primary>SCSI</primary></indexterm>
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<indexterm><primary>BIOS</primary></indexterm>
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<para>More expensive systems with SCSI controllers often include BIOS
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extensions which allow the SCSI drives to be re-ordered in a similar
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fashion for up to seven drives.</para>
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<para>A user who is accustomed to taking advantage of these features may
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become surprised when the results with FreeBSD are not as expected.
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FreeBSD does not use the BIOS, and does not know the <quote>logical BIOS
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drive mapping</quote>. This can lead to very perplexing situations,
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especially when drives are physically identical in geometry, and have
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also been made as data clones of one another.</para>
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<para>When using FreeBSD, always restore the BIOS to natural drive
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numbering before installing FreeBSD, and then leave it that way. If you
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need to switch drives around, then do so, but do it the hard way, and
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open the case and move the jumpers and cables.</para>
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<sidebar>
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<title>An Illustration from the Files of Bill and Fred's Exceptional
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Adventures:</title>
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<para>Bill breaks-down an older Wintel box to make another FreeBSD box
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for Fred. Bill installs a single SCSI drive as SCSI unit zero and
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installs FreeBSD on it.</para>
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<para>Fred begins using the system, but after several days notices that
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the older SCSI drive is reporting numerous soft errors and reports
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this fact to Bill.</para>
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<para>After several more days, Bill decides it is time to address the
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situation, so he grabs an identical SCSI drive from the disk drive
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<quote>archive</quote> in the back room. An initial surface scan
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indicates that
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this drive is functioning well, so Bill installs this drive as SCSI
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unit four and makes an image copy from drive zero to drive four. Now
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that the new drive is installed and functioning nicely, Bill decides
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that it is a good idea to start using it, so he uses features in the
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SCSI BIOS to re-order the disk drives so that the system boots from
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SCSI unit four. FreeBSD boots and runs just fine.</para>
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<para>Fred continues his work for several days, and soon Bill and Fred
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decide that it is time for a new adventure -- time to upgrade to a
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newer version of FreeBSD. Bill removes SCSI unit zero because it was
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a bit flaky and replaces it with another identical disk drive from
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the <quote>archive.</quote> Bill then installs the new version of FreeBSD onto the
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new SCSI unit zero using Fred's magic Internet FTP floppies. The
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installation goes well.</para>
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<para>Fred uses the new version of FreeBSD for a few days, and certifies
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that it is good enough for use in the engineering department...it is
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time to copy all of his work from the old version. So Fred mounts
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SCSI unit four (the latest copy of the older FreeBSD version). Fred
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is dismayed to find that none of his precious work is present on SCSI
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unit four.</para>
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<para>Where did the data go?</para>
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<para>When Bill made an image copy of the original SCSI unit zero onto
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SCSI unit four, unit four became the <quote>new clone,</quote>
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When Bill
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re-ordered the SCSI BIOS so that he could boot from SCSI unit four, he
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was only fooling himself. FreeBSD was still running on SCSI unit zero.
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Making this kind of BIOS change will cause some or all of the Boot and
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Loader code to be fetched from the selected BIOS drive, but when the
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FreeBSD kernel drivers take-over, the BIOS drive numbering will be
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ignored, and FreeBSD will transition back to normal drive numbering.
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In the illustration at hand, the system continued to operate on the
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original SCSI unit zero, and all of Fred's data was there, not on SCSI
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unit four. The fact that the system appeared to be running on SCSI
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unit four was simply an artifact of human expectations.</para>
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<para>We are delighted to mention that no data bytes were killed or
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harmed in any way by our discovery of this phenomenon. The older SCSI
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unit zero was retrieved from the bone pile, and all of Fred's work was
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returned to him, (and now Bill knows that he can count as high as
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zero).</para>
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<para>Although SCSI drives were used in this illustration, the concepts
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apply equally to IDE drives.</para>
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</sidebar>
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</sect2>
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</sect1>
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<sect1 id="install-steps">
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<title>Allocating Disk Space</title>
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