Logical Volume Manager (LVM)

This is a quick and dirty cheat sheet on LVM using Linux, I have highlighted many of the common attributes for each command however this is not an extensive list, make sure you look up the command.

With the pvs, vgs and lvs commands, the number of verboses added the more verbose information for example pvs -vvvvv

Directory and Files
Directories and Files ## Directories
/etc/lvm                    - default lvm directory location
/etc/lvm/backup         - where the automatic backups go
/etc/lvm/cache          - persistent filter cache
/etc/lvm/archive        - where automatic archives go after a volume group change
/var/lock/lvm             - lock files to prevent metadata corruption

# Files
/etc/lvm/lvm.conf       - main lvm configuration file
$HOME/.lvm               - lvm history
Tools
diagnostic lvmdump
lvmdump -d <dir>
dmsetup [info|ls|status]

Note: by default the lvmdump command creates a tar ball
Physical Volumes
display

pvdisplay -v
pvs -v
pvs -a
pvs --segments (see the disk segments used)

pvs attributes are:
1. (a)llocatable
2. e(x)ported

scanning pvscan -v

Note: scans for disks for non-LVM and LVM disks
adding pvcreate /dev/sdb1

## Create physical volume with specific UUID, used to recover volume groups (see miscellaneous section)
pvcreate --uuid <UUID> /dev/sdb1

Common Attributes that you may want to use:

-M2 create a LVM2 physical volume
removing pvremove /dev/sdb1
checking pvck -v /dev/sdb1

Note: check the consistency of the LVM metadata
change physical attributes

## do not allow allocation of extents on this drive
pvchange -x n /dev/sdb1

Common Attributes that you may want to use:

--addtag add a tag
-x allowed to allocate extents
-u change the uuid

moving pvmove -v /dev/sdb2 /dev/sdb3

Note: moves any used extents from this volume to another volume, in readiness to remove that volume. However you cannot use this on mirrored volumes, you must convert back to non-mirror using "lvconvert -m 0"
Volume Groups
display vgdisplay -v
vgs -v
vgs -a -o +devices

vgs flags:
#PV - number of physical devices
#LV - number of configured volumes        

vgs attributes are:
1. permissions (r)|(w)
2. resi(z)eable
3. e(x)ported
4. (p)artial
5. allocation policy - (c)ontiguous, c(l)ing, (n)ormal, (a)nywhere, (i)nherited
6. (c)luster
scanning vgscan -v
creating

vgcreate VolData00 /dev/sdb1 /dev/sdb2 /dev/sdb3
vgcreate VolData00 /dev/sdb[123]

## Use 32MB extent size
vgcreate VolData00 -s 32 /dev/sdb1

Common Attributes that you may want to use:

-l  maximum logical volumes
-p maximum physical volumes
-s physical extent size (default is 4MB)
-A autobackup

extending vgextend VolData00 /dev/sdb3
reducing vgreduce VolData00 /dev/sdb3

vgreduce --removemissing --force VolData00
removing vgremove VolData00

Common Attributes that you may want to use:

-f force the removal of any logical volumes
checking vgck VolData00

Note: check the consistency of the LVM metadata
change volume attributes vgchange -a n VolData00

Common Attributes that you may want to use:

-a control availability of volumes within the group
-l  maximum logical volumes
-p maximum physical volumes
-s physical extent size (default is 4MB)
-x resizable yes or no (see VG status in vxdisplay)
renaming vgrename VolData00 Data_Vol_01

note: the volume group must not have any active logical volumes
converting metadata type vgconvert -M2 VolData00

Note: vgconvert allows you to convert from one type of metadata format to another for example from LVM1 to LVM2
merging vgmerge New_Vol_Group Old_Vol_Group

Note: the old volumes group will be merged into the new volume group
spliting vgsplit Old_Vol_Group New_Vol_Group [physical volumes] [-n logical volume name]
importing vgimport VolData00

Common Attributes that you may want to use:

-a import all exported volume groups
exporting ## to see if a volume has already been export use "vgs" and look at the third attribute should be a x
vgexport VolData00

Common Attributes that you may want to use:

-a export all inactive volume groups
backing up ## Backup to default location (/etc/lvm/backup)
vgcfgbackup VolData00

# Backup to specific location
vgcfgbackup -f /var/backup/VolData00_bkup VolData00

Note: the backup is written in plain text and are by default located in /etc/lvm/backup
restoring vgcfgrestore -f /var/backup/VolData00_bkup VolData00

Common Attributes that you may want to use:

-l list backups of file
-f backup file
-M metadataype 1 or 2
cloning vgimportclone /dev/sdb1

Note: used to import and rename duplicated volume group
special files vgmknodes VolData00

Note: recreates volume group directory and logical volume special files in /dev
Logical Volumes
display

lvdisplay -v
lvdisplay --maps      display mirror volumes

lvs -v
lvs -a -o +devices

## lvs commands for mirror volumes
lvs -a -o +devices
lvs -a -o +seg_pe_ranges --segments

lvs attributes are:
1. volume type: (m)irrored, (M)irrored without initail sync, (o)rigin, (p)vmove, (s)napshot, invalid (S)napshot, (v)irtual, mirror (i)mage
                      mirror (I)mage out-of-sync, under (c)onversion
2. permissions: (w)rite, (r)ead-only
3. allocation policy - (c)ontiguous, c(l)ing, (n)ormal, (a)nywhere, (i)nherited
4. fixed (m)inor
5. state: (a)ctive, (s)uspended, (I)nvalid snapshot, invalid (S)uspended snapshot, mapped (d)evice present with-out tables,
             mapped device present with (i)nactive table
6. device (o)pen (mounted in other words)

scanning lvscan -v
lvmdiskscan
creating

## plain old volume
lvcreate -L 10M VolData00

## plain old volume but with a specific name web01
lvcreate -L 10M -n web01 VolData00

## plain old volume but on a specific disk
lvcreate -L 10M VolData00 /dev/sdb1

## a striped volume called lvol1 (note the captial i for the stripe size)
lvcreate -i 3 -I 32 -L 24M -n lvol1 vg01

## Mirrored volume
lvcreate -L 10M -m1 -n data01 vg01

## Mirrored volume without a mirror log file
lvcreate -L 10M -m1 --mirrorlog core -n data01 vg01

Common Attributes that you may want to use:

-L size of the volume [kKmMgGtT]
-l number of extents
-C contiguous [y|n]
-i stripes
-I stripe size
-m mirrors
--mirrorlog
-n volume name
extending

lvextend -L 20M /dev/VolData00/vol01

Common Attributes that you may want to use:

-L size of the volume [kKmMgGtT]
-l number of extents
-C contiguous [y|n]
-i stripes
-I stripe size

Note: you can extend a ext2/ext3 filesystem using the "resize2fs" or "fsadm" command

fsadm resize /dev/VolData01/data01
resize2fs -p /dev/mapper/VolData01-data01 [size]

The -p option displays bars of progress while extendingthe filesystem

reducing/resizing

lvreduce -L 5M /dev/VolData00/vol01
lvresize -L 5M /dev/VolData00/vol01

Note: rounding will occur when extending and reducing volumes to the next extent (4MB by default), you can use resize2fs or fsadm to shrink the filesystem

fsadm resize /dev/VolData01/data01 [size]
resize2fs -p /dev/mapper/VolData01-data01 [size]

removing lvremove /dev/VolData00/vol01
adding a mirror to a non-mirrored volume lvconvert -m1 --mirrorlog core /dev/VolData00/vol01 /dev/sdb2
change volume attributes

lvchange -a n /dev/VolData00/vol01

Common Attributes that you may want to use:

-a availability
-C contiguous [y|n]
renaming lvrename /dev/VolData00/vol_old /dev/VolData00/vol_new
snapshotting lvcreate --size 100M --snapshot -name snap /dev/vg01/data01
Miscellaneous
Simulating a disk failure dd if=/dev/zero of=/dev/sdb2 count=10
reparing a failed mirror no LVM corruption ## check volume, persume /dev/sdb2 has failed
lvs -a -o +devices

# remove the failed disk from the volume (if not already done so) , this will convert volume into a non-mirrored volume
vgreduce --removemissing --force VolData00

## replace the disk physically, remember to partion it with type 8e
fdisk /dev/sdb
........

## add new disk to LVM
pvcreate /dev/sdb2

## add the disk back into volume group
vgextend VolData00 /dev/sdb2

## mirror up the volume
lvconvert -m1 --mirrorlog core /dev/VolData00/vol02 /dev/sdb2
corrupt LVM metadata without replacing drive # attempt to bring the volume group online
vgchange -a y VolData00

# Restore the LVM configation
vgcfgrestore VolData00

# attempt to bring the volume grou online
vgchange -a y VolData00

# file system check
e2fsck /dev/VolData00/data01
corrupt LVM metadata but replacing the faulty disk

# attempt to bring the volume group online but you get UUID conflict errors make note of the UUID number
vgchange -a y VolData00
vgchange -a n VolData00

## sometimes it my only be a logical volume problem
lvchange -a y /dev/VolData00/web02
lvchange -a n /dev/Voldata00/web02

## replace the disk physically, remember to partion it with type 8e
fdisk /dev/sdb
........

# after replacing the faulty drive the disk must have the previuos UUID number or you can get it from /etc/lvm directory
pvcreate --uuid <previous UUID number taken from above command> /dev/sdb2

# Restore the LVM configation
vgcfgrestore VolData00

# attempt to bring the volume group online or logical volume
vgchange -a y VolData00
lvchange -a y /dev/VolData00/web02

# file system check
e2fsck /dev/VolData00/data01

Note: if you have backed the volume group configuration you can obtain the UUID number in the backup file by default located in /etc/lvm/backup or running "pvs -v"

For other LVM's and Array utilities see my LVM central page