Introduction
Setup
to include: http://wiki.bluelightav.org/display/BLUE/LVM+Howto
On Debian and Ubuntu
In the examples the LVM physical volume (PV) is md1.
To name a volume group, please use the first two components of the hostname, separtated by dot (.), for example ac001.blue, for the naming convention please look at http://wiki.bluelightav.org/x/ewEW
To create more volume groups, use the same beginning and add _(description), where description is a meaningful identifier, for example ac001.blue_2TB_backup
Create the physical volume (PV)
Note: this step can be omitted; it is implied by the next step.
pvcreate /dev/md1
Create the volume group (VG)
vgcreate ac001.blue /dev/md1
Create logical volumes (LVs)
Here we are going to create an LV for swap. 10G gives the size of the volume (10 GB)
lvcreate -L 10G -n root ac001.blue
If you want to create other volume, check the space left on the group with the following command:
vgs
To add another volume redo the lvcreate step.
Format a logical volume (LV)
For a file system. The example formats the LV with JFS, Blue Light's standard file system other than for the /boot partition:
mkfs.jfs /dev/ac001.blue/root
For a swap device:
mkswap /dev/ac001.blue/swap
Resize a logical volume (LV)
http://wiki.bluelightav.org/display/BLUE/How+to+resize+LVM+partitions
Rename a logical volume (LV)
Umount any file system contained by the LV and rename
umount <device> lvrename <vgname> <oldlvname> <newlvname>
Activate LVMs
vgchange -ay
Recover a deleted LV
It can happen that you want to restore a deleted LV (deleted with lvremove). It is possible 
The data are on the disk, actually the changes you do on your LVMs are located in the first bytes of the partition.
First run a pvscan do check if something is available.
pvscan
You can also check for the changes made on the LVMs replacing sda4 by the partition containing the LVMs
pvck -d -v /dev/sda4
Then the next part is a bit tricky, as you need to located the changes made on the LVMs and restore the good one.
You can either do as in the following link using hexadecimal: http://blog.adamsbros.org/2009/05/30/recover-lvm-volume-groups-and-logical-volumes-without-backups/
Or use Sam's method... If you decide so, follow me 
The method explained in the link didn't work for me or I missed something. The calculated hexadecimal offset was not corresponding to the start of the needed sections even though the hex was correctly calculated. So I did it manually
Do a less of the partition and move up to section containing the data you are looking for:
less -f /dev/sda4
the section will look like that:
raspberry {
id = "V06yZ8-pHGl-CCq7-B8zl-UUVO-RmCx-sHT1je"
seqno = 5
status = ["RESIZEABLE", "READ", "WRITE"]
flags = []
extent_size = 8192
max_lv = 0
max_pv = 0
physical_volumes {
pv0 {
id = "x1U1YI-PpqQ-wDDS-r32a-TOgJ-kEsv-FhlAso"
device = "/dev/sda5"
status = ["ALLOCATABLE"]
flags = []
dev_size = 1951567872
pe_start = 384
pe_count = 238228
}
}
logical_volumes {
root {
id = "Pn30BB-pBQT-1myN-LGq6-CqUq-E3fU-dsa5Iv"
status = ["READ", "WRITE", "VISIBLE"]
flags = []
segment_count = 1
segment1 {
start_extent = 0
extent_count = 7152
type = "striped"
stripe_count = 1 # linear
stripes = [
"pv0", 0
]
}
}
var {
id = "9i2TV0-JYZe-2ghb-Lf9n-k5f8-w1jE-5Vvion"
status = ["READ", "WRITE", "VISIBLE"]
flags = []
segment_count = 1
segment1 {
start_extent = 0
extent_count = 2384
type = "striped"
stripe_count = 1 # linear
stripes = [
"pv0", 7152
]
}
}
home {
id = "taFnuT-k6WB-Bnsu-jpNG-oOXA-yOmo-YTQodP"
status = ["READ", "WRITE", "VISIBLE"]
flags = []
segment_count = 1
segment1 {
start_extent = 0
extent_count = 4768
type = "striped"
stripe_count = 1 # linear
stripes = [
"pv0", 9536
]
}
}
data {
id = "Nh5Y4K-62W7-U22c-oSYZ-5oM5-tjZr-lmCOd0"
status = ["READ", "WRITE", "VISIBLE"]
flags = []
segment_count = 1
segment1 {
start_extent = 0
extent_count = 119209
type = "striped"
stripe_count = 1 # linear
stripes = [
"pv0", 14304
]
}
}
}
}
# Generated by LVM2 version 2.02.66(2) (2010-05-20): Wed Nov 21 06:05:21 2012
contents = "Text Format Volume Group"
version = 1
description = ""
creation_host = "raspberry" # Linux raspberry 3.2.0-23-generic-pae #36-Ubuntu SMP Tue Apr 10 22:19:09 UTC 2012 i686
creation_time = 1353477921 # Wed Nov 21 06:05:21 2012
Above you can see the different LV present: root, data, var, swap
To find out the step before the deletion of an LV just look at the difference between 2 sections. If one LV is missing in one section it means the previous section is the one you want. Hope I'm clear. If not just figure it out or ask
As explained in the earlier link, the seqno value will indicate you if the size has been changed.
Once you have found the right section, copy it to a file on your disk. You need to copy from the VG name to after the creation time (as shown in the above code piece)
Then run the following command replacing what is necessary to be replaced:
vgcfgrestore -f <name_of_created_data_file> -v <LV_name>
If the restored LVs are not active use:
vgchange -ay --ignorelockingfailure
You are done
Outdated
Resize existing file system without LiveCD
pvs PV VG Fmt Attr PSize PFree /dev/sda3 rose lvm2 a- 144.85G 44.85G lvm lvm> lvs LV VG Attr LSize Origin Snap% Move Log Copy% home rose -wi-ao 50.00G opt rose -wi-ao 10.00G root rose -wi-ao 10.00G tmp rose -wi-ao 10.00G var rose -wi-ao 20.00G lvm> lvresize -L +30G /dev/rose/home Extending logical volume home to 80.00 GB Logical volume home successfully resized lvm> quit Exiting. resize_reiserfs -s +30G /dev/rose/home df -h Filesystem Size Used Avail Use% Mounted on /dev/mapper/rose-home 80G 49G 32G 61% /home
Using LVM on Live CD
here is a great howto getting LVM working.
what I did here was
aptitude install lvm2 dmsetup modprobe dm-mod pvscan vgscan vgchange -a y
and all the lvm's are active and mountable
LVM on RAID
A great howto is here http://www.gagme.com/greg/linux/raid-lvm.php
Chrooting and installing GRUB 2 on LVM setup
Boot with a live CD or CrowBar
mkdir /mnt/root mount /dev/mapper/volume_group_name-root /mnt/root mount /dev/mapper/volume_group_name-home /mnt/root/home mount /dev/mapper/volume_group_name-var /mnt/root/var mount /dev/sda1 /mnt/root/boot mount -t proc none /mnt/root/proc mount --bind /dev /mnt/root/dev mount --bind /sys /mnt/root/sys chroot /mnt/root update-initramfs -u update-grub grub-install /dev/sda