You will want to make sure Multi device support (RAID and LVM) is enabled and LVM support is compiled into your kernel. You could build it as a module and load it from your initrd, but you don't really need to go to the effort.
You have a 36gb disc (this might be a RAID logical volume already, but the system sees it as one disc with 36gb on it). You want to install partitions for /usr, /var etc (smart) but you're not sure what sizes they need to be and you will want to be able to resize them in future.
At install time, create a small (<100mb) /boot, swap, and a reasonable (4-6gb) / partition. Leave the rest of the space unpartitioned.
Make sure LVM is compiled into your kernel, and you have the LVM tools installed. Debian 3 (woody): install lvm10. Debian Sarge/Sid: install lvm2.
Gentoo has lvm (1.01) and lvm2. You may also need the device-mapper patch for 2.4.x kernels, available at 
ftp://sources.redhat.com/pub/dm/. From the LVM2 README.Debian:
LVM2 requires the device-mapper kernel module (dm-mod). This is available as a kernel patch for 2.4 (included as standard in current Debian 2.4 kernels), and is distributed with linux 2.5 and above.
Apply the patch with something like
# patch -p1 /path/device-mapper.1.01.03/patches/linux-2.4.28-pre4-devmapper-ioctl.patch
# fdisk /dev/sda
Set the type of this partition (which, in my case, is primary partition 4 and eats the rest of my disc) to 8e - Linux LVM.
First, run vgscan:
# vgscan
vgscan -- reading all physical volumes (this may take a while...)
vgscan -- "/etc/lvmtab" and "/etc/lvmtab.d" successfully created
vgscan -- WARNING: This program does not do a VGDA backup of your volume group 4?
This creates a volume group descriptor area (VGDA) at the start of the disks.
# pvcreate /dev/sda4 pvcreate -- physical volume "/dev/sda4" successfully created
This volume group can contain multiple discs, but in this case it only uses one.
# vgcreate lvmarray /dev/sda4 vgcreate -- INFO: using default physical extent size 4 MB vgcreate -- INFO: maximum logical volume size is 255.99 Gigabyte vgcreate -- doing automatic backup of volume group "lvmarray" vgcreate -- volume group "lvmarray" successfully created and activated # vgdisplay
Confirm that the VG size is the right amount for the size of the partition.
Note that if you use devfs, you'll need to use the full devfs pathname, not the /dev/sda4 symlink. EG:, use /dev/scsi/host0/bus0/target0/lun0/part4 instead of /dev/sda4
# lvcreate -L20G -nhome lvmarray lvcreate -- doing automatic backup of "lvmarray" lvcreate -- logical volume "/dev/lvmarray/home" successfully created # lvcreate -L5G -nvar lvmarray lvcreate -- doing automatic backup of "lvmarray" lvcreate -- logical volume "/dev/lvmarray/var" successfully created # lvcreate -L5G -nusr lvmarray lvcreate -- only 793 free physical extents in volume group "lvmarray" # lvcreate -L793 -nusr lvmarray lvcreate -- rounding size up to physical extent boundary lvcreate -- doing automatic backup of "lvmarray" lvcreate -- logical volume "/dev/lvmarray/usr" successfully created
# for i in home var usr; do mke2fs -j /dev/lvmarray/$i; done
(Now would be a good time to learn about label based mounting!)
mount /dev/lvmarray/home /home
You will of course want to move everything from /home first, and add them to fstab(5) etc... To move your partitions, you'll probably want to be in runlevel 1.
If you get an this error message with the above command:
mount: special device /dev/lvmarray/home does not exist
then you may need to use "vgchange -ay" to activate the logical volumes. This can happen if you are booting to a LiveCD or have rebooted after creating the logical volumes.
Oops! Just created 20g /home, 5gb /var and 860mb /usr. So lets take 4gb from home and add it to usr.
# umount /home # e2fsadm -L-4G /dev/lvmarray/home # mount /home # umount /usr # e2fsadm -L+4G /dev/lvmarray/usr # mount /usr
e2fsadm is a utility that comes with LVM that lets you automatically fsck, resize FS and then resize LV.
# e2fsadm -L+1G /foo
is equivalent to the two commands:
# lvextend -L+1G /foo # resize2fs /foo
You need to have e2fsprogs installed for this to work (but you probably needed it to make the FS to start with.)
When the time comes to learn to resize LVM partitions, there'll be more. Until then, see 
http://tldp.org/HOWTO/LVM-HOWTO
If you are upgrading from a 2.4 to a 2.6 kernel and you have an LVM1 partition, you must install the 'lvm2' package.
There are two version of LVM:
[1] PV: Physical Volume; a disc or a partition on a disc. [2] VG: Volume Group; a group of one-or-more physical volumes across which you get a "virtual disk", a space to create logical volumes in. [3] LV: Logical Volume; something you eventually create an FS on. [4] To create a VGDA (Volume Group Descriptor Area) backup, use !vgcfgbackup(8)?.
Found this one on a new Ubuntu install. /boot is on a separate partition to the LVM (which you should always do, as LILO/GRUB aren't good at booting off an LVM volume).
The installer has written an LVM checksum to /boot, and LVM tools are confused when they see it.
So, edit /etc/lvm/lvm.conf - change
filter = [ "r|/dev/cdrom|" ]
to
filter = [ "r|/dev/cdrom|", "r|/dev.*hda1|" ]
The regexp match is to catch both /dev/hda1 and /dev/evms/hda1.
