Put portage stuff on LVM

Recently I installed LVM2 on /dev/hda3.
First use fdisk to change partition type for /dev/hda3 to 8e (Linux LVM)(turns out this is unnecessary when using LVM 2, but still a good thing for disk management).
Recompile kernel:

Device Drivers  --->
 Multi-device support (RAID and LVM)  --->
   [*] Multiple devices driver support (RAID and LVM)
   < >   RAID support
   <*>   Device mapper support
   < >     Crypt target support

If "Device mapper support" is compiled as a module, add the module "dm-mod" to /etc/modules.autoload.d/kernel-2.6.
Install the lvm2 package:

# emerge lvm2

Edit /etc/lvm/lvm.conf, find the line:

 filter = [ "a/.*/" ]

Replace it with the following one to scan /dev/hda and /dev/hdb and reject anything else:

 filter = [ "a|/dev/hd[ab]|", "r/.*/" ]

Then reboot. Now prepare the partition:

# pvcreate /dev/hda3

This creates a volume group descriptor at the start of the /dev/hda3 partition.
Create a volume group named "vg":

# vgcreate vg /dev/hda3

Create the logical volumes (just like creating partitions with fdisk):

# lvcreate -L3G -nportage  vg
# lvcreate -L3G -nccache vg
# vgdisplay vg | grep Free
Free  PE / Size       667 / 2.61 GB
# lvcreate -l 667 vg -n tmp (let "tmp" take up all the rest)

Now you should see portage, ccache and tmp in /dev/vg/
Create filesystems on the logical volumes:

# mkreiserfs /dev/vg/portage
# mkreiserfs /dev/vg/ccache
# mkreiserfs /dev/vg/tmp

Move the stuff in /usr/portage, /var/tmp/ccache and /var/tmp/portage to another place and mount the logical volumes, then move the stuff back:

# mv /usr/portage/* /root/portage
# mv /var/tmp/ccache/* /root/ccache
# mv /var/tmp/portage/* /root/tmp
# mount /dev/vg/portage /usr/portage
# mount /dev/vg/tmp /var/tmp/portage
# mount /dev/vg/ccache /var/tmp/ccache
# mv /root/portage/* /usr/portage
# mv /root/ccache/* /var/tmp/ccache
# mv /root/tmp/* /var/tmp/portage

Add the following lines to /etc/fstab:

# Logical volumes
/dev/vg/portage    /usr/portage      reiserfs  noatime   0 0
/dev/vg/ccache     /var/tmp/ccache   reiserfs  noatime   0 0
/dev/vg/tmp        /var/tmp/portage  reiserfs  noatime   0 0

Then if you restart your machine, all partitions will be automatically mounted.

Here comes the nice things about LVM, shrink logical volume "portage":

# umount /usr/portage/
# resize_reiserfs -s-1500M /dev/vg/portage (First, resize the filesystem)
# lvreduce -L-1500M /dev/vg/portage (resize the logical volume)
# mount /usr/portage

To extend a logical volume, we do it in a slightly different order:

# lvextend -L+1G /dev/vg/portage
# resize_reiserfs -f /dev/vg/portage (no need to umount nor specify size this time)

To add another physical partition to the volume group "vg":

# pvcreate /dev/hda9
# vgextend vg /dev/hda9

then you should be able to create more logical volumes.

Other useful commands:

# umount /dev/vg/tmp 
# lvremove /dev/vg/tmp (remove a logical volume)
# vgreduce vg /dev/hda9 (remove a physical volume from a group)
# vgchange -a n vg (deactivate a volume group)
# vgremove vg (remove a volume group)

P.S. I'm now thinking about the following scheme for dealing with portage stuff:
1) put /usr/portage on a reiserfs LV, perhaps 300MB is enough.

2) put sources in a directory other than /usr/portage/distfiles, probably /var/distfiles (may be on an independent ext3 LV).

3) put /var/tmp (which includes /var/tmp/ccache and /var/tmp/portage) on an ext2 LV, maybe 5G?