Introduction

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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, separated 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

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LVM creates virtual block devices out of other block devices.  In the simplest case, "other block devices" are hard disk partitions.  LVM calls them "physical volumes" or PVs.

LVM groups physical volumes into volume groups (VGs).

From the volume groups' pool of blocks, LVM creates virtual block devices which it calls "logical volumes" or LVs.

Here's a diagram of all that:

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In the standard Blue Light setup, the physical volumes are not disk partitions but Multiple devices (md, software RAID) devices.

Setup

In the examples the LVM physical volume (PV) is md1.

Create a physical volume (PV)

Note: this step can be omitted; it is implied by the next step.

pvcreate /dev/md1

Create

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a volume group (VG)

The volume group name was normally the first two components of the hostname separated by dot; now we use the FQDN.

vgcreate ac001ltsp.blueth /dev/md1

The Blue Light volume group naming convention is designed to ensure names which are unique amongst computers we support.  This allows us to put HDDs containing LVM storage in any computer for recovery purposes.

Create logical volumes (LVs)

Here we are going to create an LV for swap. 10G gives the size of the volume (10 GB)For example (10G gives a 10 GB size):

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.

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ltsp.th

Operations

Show current LVM usage

Overall picture: lsblk (not available on Debian 6)

Show PVs: pvs

Show VGs: vgs

Show LVs: lvs

Activate LVM volume groups (VGs)

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Format a logical volume (LV)

This is exactly the same as formatting any other sort of block device; only the device file path is LV-specific, for example /dev/ltsp.

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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

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th/root

Extend a logical volume (LV)

In case multiple PVs are being used to minimise the effect of storage device failure, keep the LV on a single PV if possible.

LVs are extended by the lvextend command.  The --help is, er, helpful.

Single PV

Extending an LV on a single PV may require moving the LV to a PV which has more space or moving other LV(s) off the initial PV.

Find which PVs are hosting each LV:

lvs -o lv_name,devices

Find how much space available on each PV:

pvs

Finally the PV is specified on the lvextend command.  Examples:

lvextend --size 400G /dev/bafi.backup/th /dev/sdc1
lvextend --extents +55172 /dev/bafi.backup/blue /dev/sdb3

Reduce a logical volume (LV)

http://wiki.bluelightav.org/display/BLUE/How+to+resize+LVM+partitions

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Use the lvreduce command.

Move storage or logical volumes (LVs) between physical volumes (PVs)

Move storage

This is useful when upgrading HDDschanging physical volumes (PVs).  After adding the new HDDs, usually as a RAID 1 md array, to the volume group, the LVs can be moved from the old PV to  the new.  Finally the old PV can be removed from the VG and the old HDDs removed, usually after powering down.

For example:

pvmove /dev/md1 /dev/md3 

Move a logical volume (LV)

For example:

pvmove --name atlassian.blue.av-disk /dev/md1 /dev/sdb1

Rename a logical volume (LV)

Umount any file system contained by the LV and rename

umount <device>
lvrename <vgname> <oldlvname> <newlvname> 

Remove a Physical Volume (PV) from a Volume Group (VG)

vgreduce VG_name PV_name

For example:

vgreduce ls1 /dev/sdb2

Troubleshooting

Messages

File descriptor * leaked on * invocation. Parent PID *

Can be safely ignored.  Can be suppressed by setting LVM_SUPPRESS_FD_WARNINGS environment variable before doing whatever produced the message.

Code to generate the message was added when it was alleged that LVM was leaking file descriptors.  The message shows that a file descriptor has already been leaked when an LVM program is called.

WARNING: lvmetad is running but disabled. Restart lvmetad before enabling it!

Can be safely ignored.

From https://wiki.gentoo.org/wiki/Talk:LVM#lvmetad_warning: "Normally lvmetad is not even enabled. Neither in initscripts nor in /etc/lvm/lvm.conf. But the lvm service has a useless rc_need on lvmetad. Remove it to get rid of those messages".

Recover a deleted logical volume (LV)

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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:

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vgchange -ay --ignorelockingfailure

You are done 

Rename a logical volume (LV)

Umount any file system contained by the LV and rename

umount <device>
lvrename <vgname> <oldlvname> <newlvname> 

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Resize existing file system without LiveCD

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A great howto is here http://www.gagme.com/greg/linux/raid-lvm.php 

Chrooting and installing GRUB 2 on LVM setup

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