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<TITLE>The Linux+FreeBSD mini-HOWTO: The FreeBSD way of labelling hard drives</TITLE>
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<H2><A NAME="s2">2. The FreeBSD way of labelling hard drives</A><!--FreeBSD dualboot!disk drive labelling--></H2>
<P>Linux and FreeBSD label hard drives and partitions after two differents
schemes. This section explains the main differences between the two schemes.
In fact the FreeBSD labelling scheme is an adaption of the traditional BSD
labelling style ported to live within the PC's fdisk partitions. Thus it is
very similar to other BSD-based Unix systems such as NetBSD, OpenBSD, Ultrix,
Digital Unix, SunOS, and Solaris.
<P>
<H2><A NAME="ss2.1">2.1 FreeBSD ``slices'' and ``partitions''</A>
<!--FreeBSD dualboot!disk drive partitions--><!--FreeBSD dualboot!disk drive slices--></H2>
<P>FreeBSD needs one of the four entries in the partition table on your PC's
hard drive. This primary partition is called a <B>``slice''</B> in FreeBSD
terminology. It then uses the <CODE>disklabel</CODE> program to make up to eight
partitions in this primary partition. These logical partitions are called
<B>``partitions''</B> in FreeBSD terminology. This concept is similar to the way
Linux (and DOS) handles logical partitions in an extended partition. You
cannot install FreeBSD in an extended partition made by Linux (or DOS). Note
that the Linux <CODE>fdisk</CODE> program doesn't display the BSD partitions in a
FreeBSD slice from the main menu, but it can display BSD disklabel information
if you give the command `b'. The output is something like this
(<CODE>/dev/hda4</CODE> is the FreeBSD slice):
<PRE>
bash# fdisk /dev/hda
Command (m for help): p
Disk /dev/hda: 64 heads, 63 sectors, 621 cylinders
Units = cylinders of 4032 * 512 bytes
Device Boot Begin Start End Blocks Id System
/dev/hda1 * 1 1 27 54400+ 83 Linux native
/dev/hda2 28 28 55 56448 83 Linux native
/dev/hda3 56 56 403 701568 83 Linux native
/dev/hda4 404 404 621 439488 a5 BSD/386
Command (m for help): b
Reading disklabel of /dev/hda4 at sector 1624897.
BSD disklabel command (m for help): p
8 partitions:
# size offset fstype [fsize bsize cpg]
a: 64512 1624896 4.2BSD 0 0 0 # (Cyl. 404 - 419)
b: 104832 1689408 swap # (Cyl. 420 - 445)
c: 878976 1624896 unused 0 0 # (Cyl. 404 - 621)
e: 64512 1794240 4.2BSD 0 0 0 # (Cyl. 446 - 461)
f: 645120 1858752 4.2BSD 0 0 0 # (Cyl. 462 - 621)
BSD disklabel command (m for help): q
bash#
</PRE>
<P>The letters `a'...`f' in the first column are the same labels as shown below
in the example for a FreeBSD slice. There are three special partitions in BSD
parlace. The letter `a' designates the root partition, `b' designates the swap
partition, while `c' designates the whole slice. See the FreeBSD documentation
for more information on the ``standard'' way of assigning these letters to
different partition types.
<P>
<H2><A NAME="ss2.2">2.2 Drive and partition labelling in Linux and FreeBSD</A>
<!--FreeBSD dualboot!disk drive labelling!compared with Linux--><!--FreeBSD dualboot!disk drive partitions!compared with Linux--></H2>
<P>The hard drives are labelled in the following way in Linux and FreeBSD:
<PRE>
Linux FreeBSD
First IDE drive /dev/hda /dev/wd0
Second IDE drive /dev/hdb /dev/wd1
First SCSI drive /dev/sda /dev/sd0
Second SCSI drive /dev/sdb /dev/sd1
</PRE>
<P>The partitions (FreeBSD slices) on an IDE drive are labelled in the following
way (<CODE>/dev/hda</CODE> is used as an example):
<PRE>
Linux FreeBSD
First primary partition /dev/hda1 /dev/wd0s1
Second primary partition /dev/hda2 /dev/wd0s2
Third primary partition /dev/hda3 /dev/wd0s3
Fourth primary partition /dev/hda4 /dev/wd0s4
</PRE>
<P>The partitions in my FreeBSD slice is labelled in the following way. It is the
labelling you get by default. It is possible to change the labelling if you do
a custom installation of FreeBSD (<CODE>/dev/hda4</CODE> is the FreeBSD slice in
the example):
<PRE>
Linux label FreeBSD label FreeBSD mount point
/dev/hda5 /dev/wd0s4a /
/dev/hda6 /dev/wd0s4b swap
/dev/hda7 /dev/wd0s4e /var
/dev/hda8 /dev/wd0s4f /usr
</PRE>
<P>If you run <CODE>dmesg</CODE> in Linux you will see this as (The linux kernel must be
build with <B>UFS filesystem support</B> for this to work. See section
<A HREF="Linux+FreeBSD-3.html#installlinux">Installing and preparing Linux</A>):
<PRE>
Partition check:
hda: hda1 hda2 hda3 hda4 < hda5 hda6 hda7 hda8 >
</PRE>
<P>If you have installed FreeBSD in the <CODE>/dev/sd1s3</CODE> slice
(<CODE>/dev/sdb3</CODE> in Linux parlace), and <CODE>/dev/sdb2</CODE> is a Linux
extended partition containing two logical partitions (<CODE>/dev/sdb5</CODE> and
<CODE>/dev/sdb6</CODE>), the previous example would look like this:
<PRE>
Linux label FreeBSD label FreeBSD mount point
/dev/sdb7 /dev/sd1s3a /
/dev/sdb8 /dev/sd1s3b swap
/dev/sdb9 /dev/sd1s3e /var
/dev/sdb10 /dev/sd1s3f /usr
</PRE>
<P>This will be shown as
<PRE>
Partition check:
sdb: sdb1 sdb2 < sdb5 sdb6 > sdb3 < sdb7 sdb8 sdb9 sdb10 >
</PRE>
in the output from <CODE>dmesg</CODE>.
<P>If you have a Linux extended partition <EM>after</EM> your FreeBSD slice you're in
for trouble, because most Linux kernels installation floppies are build
without UFS support, they will not recognise the FreeBSD partitions inside the
slice. What should have have been seen as (<CODE>/dev/hda3</CODE> is the FreeBSD
slice and <CODE>/dev/hda4</CODE> is the Linux extended partition)
<PRE>
Partition check:
hda: hda1 hda2 hda3 < hda5 hda6 hda7 hda8 > hda4 < hda9 hda10 >
</PRE>
is seen as:
<PRE>
Partition check:
hda: hda1 hda2 hda3 hda4 < hda5 hda6 >
</PRE>
<P>This can give you the wrong device assignment and cause the loss of data. My
advice is to <EM>always put your FreeBSD slice after any Linux extended
partitions, and do not change any logical partitions in your Linux extended
partitions after installing FreeBSD!</EM>
<P>
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