---
title: Howto LVM
category: linux disk
...
*
LVM est un système permettant de gérer des "logical volumes" (LV) indépendamment des disques.
On obtient ainsi un système de partitionnement plus souple, cela facilite notamment l'augmentation (future) de la taille d'un LV.
## Installation
~~~
# apt install lvm2
~~~
### PV : les partitions LVM
On doit ensuite créer des partitions de type "Linux LVM" (code `8E`).
Puis on initialise les partitions pour LVM :
~~~
# pvcreate /dev/hda1
# pvcreate /dev/hdb1
~~~
**Note** : dans certains cas, on devra utiliser l'option `-ff` (par exemple pour réinitialiser une partition)
On pourra ainsi liste les partitions LVM du système avec `pvdisplay` ou `pvs` :
~~~
# pvdisplay
--- Physical volume ---
PV Name /dev/hda1
VG Name group1
PV Size 124.84 GB / not usable 1.52 MB
Allocatable yes
PE Size (KByte) 4096
Total PE 31959
Free PE 7639
Allocated PE 24320
PV UUID T12qj5-SEkv-zNrB-QUdG-tFua-b6ok-p1za3e
--- Physical volume ---
PV Name /dev/hdb1
VG Name group1
PV Size 13.08 GB / not usable 2.08 MB
Allocatable yes
PE Size (KByte) 4096
Total PE 3347
Free PE 3347
Allocated PE 0
PV UUID CQEeDw-TYNK-n0nh-G7ti-3U3J-4zgk-a7xg2S
# pvs
PV VG Fmt Attr PSize PFree
/dev/hda1 group1 lvm2 a- 13.07G 13.07G
/dev/hdb1 group1 lvm2 a- 124.84G 34.84G
# pvs -o pv_mda_count,pv_mda_free /dev/hda1
#PMda #PMdaFree
1 91.50K
# pvscan
PV /dev/sda9 VG group1 lvm2 [124.84 GB / 29.84 GB free]
PV /dev/sda12 VG group1 lvm2 [13.07 GB / 13.07 GB free]
Total: 2 [137.91 GB] / in use: 2 [137.91 GB] / in no VG: 0 [0 ]
~~~
Si la partition est redimensionnée, on peut augmenter la taille du PV :
~~~
# pvresize /dev/hda1
~~~
### VG : les groupes de volumes
Une fois nos PV initialisés, on crée un ou plusieurs groupes de volumes (VG) dans lequels on découpera les volumes logiques (LV).
~~~
# vgcreate group1 /dev/hda1 /dev/hdb1
Volume group "mylvmtest" successfully created
~~~
On peut ainsi les lister avec les commande `vgdisplay` ou `vgs` :
~~~
# vgdisplay
--- Volume group ---
VG Name group1
System ID
Format lvm2
Metadata Areas 2
Metadata Sequence No 28
VG Access read/write
VG Status resizable
MAX LV 0
Cur LV 5
Open LV 4
Max PV 0
Cur PV 2
Act PV 2
VG Size 137.91 GB
PE Size 4.00 MB
Total PE 35306
Alloc PE / Size 24320 / 95.00 GB
Free PE / Size 10986 / 42.91 GB
VG UUID zwApn7-SCSx-ju4h-6Y1R-x6ie-3wl0-uSE1DE
# vgs
VG #PV #LV #SN Attr VSize VFree
group1 2 5 0 wz--n- 137.91G 42.91G
# vgscan
Reading all physical volumes. This may take a while...
Found volume group "group1" using metadata type lvm2
~~~
### LV : les volumes logiques
On peut maintenant découper nos volumes finaux :
~~~
# lvcreate -L5G -nfirstlvmvol group1
Logical volume "firstlvmvol" created
# lvcreate -L10G -nsecondlvmvol group1
Logical volume "secondlvmvol" created
~~~
On a ainsi des périphériques de stockage utilisables (accessibles via `/dev/mapper/-` ou `/dev//`) que l'on peut formater :
~~~
# mkfs.ext4 /dev/mapper/group1-firstlvmvol
# mkfs.ext4 /dev/group1/secondlvmvol
~~~
On peut lister les LV avec `lvdisplay` ou `lvs` :
~~~
# lvdisplay
--- Logical volume ---
LV Name /dev/group1/firstlvmvol
VG Name group1
LV UUID iHCvHy-ow0G-Idf2-hNOi-TRFe-BqvW-tmowLj
LV Write Access read/write
LV Status available
# open 1
LV Size 5.00 GB
Current LE 2560
Segments 1
Allocation inherit
Read ahead sectors auto
- currently set to 256
Block device 253:0
--- Logical volume ---
LV Name /dev/group1/secondlvmvol
VG Name group1
LV UUID S5GPY7-7q6n-1FCy-ydKA-Js2e-BAOy-wlgYQO
LV Write Access read/write
LV Status available
# open 1
LV Size 10.00 GB
Current LE 12800
Segments 1
Allocation inherit
Read ahead sectors auto
- currently set to 256
Block device 253:1
# lvs
LV VG Attr LSize Origin Snap% Move Log Copy% Convert
firstlvmvol group1 -wi-ao 5.00G
secondlvmvol group1 -wi-ao 10.00G
# lvscan
ACTIVE '/dev/group1/firstlvmvol' [5.00 GB] inherit
ACTIVE '/dev/group1/secondlvmvol' [10.00 GB] inherit
~~~
### Les snapshots LVM
Un snapshot LVM sert à "figer" une partition à chaud, par exemple pour pouvoir faire une vraie sauvegarde "tranquillement" par la suite.
Exemple typique, une base SQL stocke ses fichiers dans `/srv/sql` qui est en LVM :
* On arrête la base SQL (ou on la "lock")
* On déclenche un snapshot LVM de `/srv/sql`
* On redémarre (ou "délock") la base SQL : elle n'aura été arrêtée que qq secondes !
* Ensuite, on peut monter le snapshot et faire tranquillement son backup (tar, dd, rsync, etc.)
* Il faut ensuite virer le snapshot (il ne survit pas à un reboot de toute façon)
**Note** : il semble qu'on peut pas trop avoir deux snapshots en même temps.
~~~
# lvcreate -L100M -s -n snap /dev/mylvmtest/firstlvmvol
Logical volume "snap" created
# lvdisplay
--- Logical volume ---
LV Name /dev/mylvmtest/firstlvmvol
VG Name mylvmtest
LV UUID 4vOXer-YH8x-AB9T-3MoP-BESB-7fyn-ce0Rho
LV Write Access read/write
LV snapshot status source of
/dev/mylvmtest/snap [active]
LV Status available
# open 0
LV Size 500.00 MB
Current LE 125
Segments 1
Allocation inherit
Read ahead sectors 0
Block device 253:0
--- Logical volume ---
LV Name /dev/mylvmtest/snap
VG Name mylvmtest
LV UUID lF0wn9-7O3A-FacC-gnVM-SPwE-fCnI-5jb9wz
LV Write Access read/write
LV snapshot status active destination for /dev/mylvmtest/firstlvmvol
LV Status available
# open 0
LV Size 500.00 MB
Current LE 125
COW-table size 100.00 MB
COW-table LE 25
Allocated to snapshot 0.02%
Snapshot chunk size 8.00 KB
Segments 1
Allocation inherit
Read ahead sectors 0
Block device 253:3
# mkdir /tmp/snap
# mount /dev/mylvmtest/snap /tmp/snap/
# lvcreate -L100M -s -n snap2 /dev/mylvmtest/firstlvmvol
Logical volume "snap2" created
device-mapper: snapshots: Invalidating snapshot: Unable to allocate exception.
Buffer I/O error on device dm-3, logical block 530
lost page write due to I/O error on dm-3
Buffer I/O error on device dm-3, logical block 530
lost page write due to I/O error on dm-3
Buffer I/O error on device dm-3, logical block 530
lost page write due to I/O error on dm-3
Buffer I/O error on device dm-3, logical block 1
lost page write due to I/O error on dm-3
Buffer I/O error on device dm-3, logical block 1
lost page write due to I/O error on dm-3
# umount /tmp/snap
# lvremove /dev/mylvmtest/snap
Do you really want to remove active logical volume "snap"? [y/n]: y
Logical volume "snap" successfully removed
~~~
### LVM mirror : du RAID1 avec LVM
Une fonctionnalité peu connue de LVM est de permettre de faire du RAID1.
Peu d'intérêt a priori. À part peut-être gérer du RAID1 "retaillable" sans gérer un couche "MDADM + LVM".
~~~
# pvcreate /dev/sda7
Physical volume "/dev/sda7" successfully created
# pvcreate /dev/sdb5
Physical volume "/dev/sdb5" successfully created
# lvcreate -L180G -m1 -nlvmirror --corelog vg00 /dev/sda7 /dev/sdb5
Logical volume "lvmirror" created
# lvs -a
LV VG Attr LSize Origin Snap% Move Log Copy%
lvmirror vg00 mwi-ao 180.00G 8.60
[lvmirror_mimage_0] vg00 iwi-ao 180.00G
[lvmirror_mimage_1] vg00 iwi-ao 180.00G
~~~
Pour étendre un miroir LVM, on ajoute des PV au VG :
~~~
# pvcreate /dev/sda8
Physical volume "/dev/sda8" successfully created
# pvcreate /dev/sdb6
Physical volume "/dev/sdb6" successfully created
# vgextend vg00 /dev/sda8 /dev/sdb6
Volume group "vg00" successfully extended
~~~
On désactive le miroir, on retaille, on réactive :
~~~
# lvextend -L+25G /dev/vg00/lvmirror
Extending 2 mirror images.
Mirrors cannot be resized while active yeta.
# umount /dev/vg00/lvmirror
# lvchange -an /dev/vg00/lvmirror
# lvextend -L+25G /dev/vg00/lvmirror
Extending 2 mirror images.
Extending logical volume lvmirror to 205.00 GB
Logical volume lvmirror successfully resized
# lvchange -ay /dev/vg00/lvmirror
~~~
Enfin on retaille le filesystem :
~~~
# e2fsck -f /dev/vg00/lvmirror
e2fsck 1.40-WIP (14-Nov-2006)
Pass 1: Checking inodes, blocks, and sizes
Pass 2: Checking directory structure
Pass 3: Checking directory connectivity
Pass 4: Checking reference counts
Pass 5: Checking group summary information
/dev/vg00/lvmirror: 216749/23592960 files (13.5% non-contiguous), 44825506/47185920 blocks
# resize2fs /dev/vg00/lvmirror
resize2fs 1.40-WIP (14-Nov-2006)
Resizing the filesystem on /dev/vg00/lvmirror to 53739520 (4k) blocks.
The filesystem on /dev/vg00/lvmirror is now 53739520 blocks long.
~~~
## FAQ
### Supprimer une partition LVM d'un VG
~~~
# pvmove -v /dev/hde1
Finding volume group "mylvmtest"
Archiving volume group "mylvmtest" metadata.
Creating logical volume pvmove0
mirror: Required device-mapper target(s) not detected in your kernel
# vgreduce mylvmtest /dev/hde1
Removed "/dev/hde1" from volume group "mylvmtest"
~~~
### Supprimer un LV
~~~
# lvremove -v /dev/testlvm/testlvm2
Using logical volume(s) on command line
Do you really want to remove active logical volume "testlvm2"? [y/n]: y
Archiving volume group "testlvm" metadata.
Found volume group "testlvm"
Removing testlvm-testlvm2
Found volume group "testlvm"
Releasing logical volume "testlvm2"
Creating volume group backup "/etc/lvm/backup/testlvm"
Logical volume "testlvm2" successfully removed
~~~
### Augmenter la taille d'un LV
~~~
# umount /dev/mylvmtest/thirdlvmvol
# lvextend -L+1G /dev/mylvmtest/thirdlvmvol
Extending logical volume thirdlvmvol to 4,00 GB
Logical volume thirdlvmvol successfully resized
# resize2fs -p /dev/mylvmtest/thirdlvmvol
# e2fsck -f /dev/mylvmtest/thirdlvmvol -C0
e2fsck 1.35 (28-Feb-2004)
Passe 1: vérification inodes, blocs, et des tailles
Passe 2: vérification de la structure répertoire
Passe 3: vérification de lca connectivité répertoire
Pass 4: vérification des compteur de références
Pass 5: vérification de l'information du sommaire groupe
/dev/mylvmtest/thirdlvmvol: 11/393216 fichier (0.0% non
blocs
# resize2fs -p /dev/mylvmtest/thirdlvmvol
resize2fs 1.35 (28-Feb-2004)
Resizing the filesystem on /dev/mylvmtest/thirdlvmvol to
Le système de fichiers /dev/mylvmtest/thirdlvmvol a main
8576 blocs.
~~~
### Réduire la taille d'un LV
~~~
ACTIVE '/dev/mylvmtest/secondlvmvol' [60,00 GB] inherit
# umount /dev/mylvmtest/secondlvmvol
# e2fsck -f /dev/mylvmtest/secondlvmvol -C0
# resize2fs /dev/mylvmtest/secondlvmvol 50G
resize2fs 1.41.12 (17-May-2010)
Resizing the filesystem on /dev/mylvmtest/secondlvmvol to 13107200 (4k) blocks.
The filesystem on /dev/mylvmtest/secondlvmvol is now 13107200 blocks long.
# lvreduce -L-10G /dev/mylvmtest/secondlvmvol
WARNING: Reducing active logical volume to 50,00 GB
THIS MAY DESTROY YOUR DATA (filesystem etc.)
Do you really want to reduce secondlvmvol? [y/n]: y
Reducing logical volume secondlvmvol to 50,00 GB
Logical volume secondlvmvol successfully resized
# mount /dev/mylvmtest/secondlvmvol
~~~
### LVM et les tailles
Les tailles reportées par LVM sont très peu fiables.
Un exemple concret avec un VG qui annonce :
~~~
VG Size 137.91 GB
PE Size 4.00 MB
Total PE 35306
Alloc PE / Size 23040 / 90.00 GB
Free PE / Size 12266 / 47.91 GB
~~~
On a donc tendance à croire qu'il reste de la place… Pourtant un `lvextend` ou `lvcreate` échoue.
Par exemple :
~~~
# lvextend -L+10G /dev/group1/data
Extending logical volume data to 30.00 GB
device-mapper: resume ioctl failed: Invalid argument
Unable to resume group1-data (253:3)
Logical volume data successfully resized
# lvcreate -L5G -ntest group1
device-mapper: resume ioctl failed: Invalid argument
Unable to resume group1-test (253:4)
/dev/group1/test: write failed after 0 of 4096 at 0: No space left on device
Logical volume "test" created
~~~
### Restauration
**/!\\ à manipuler avec beaucoup de précautions /!\\**
LVM sauvegarde ses métadatas dans `/etc/lvm/backup` et `/etc/lvm/archive`.
On peut éventuellement les restaurer via la commande `vgcfgrestore`.
### Infos sur les volumes
~~~
# dmestup info -c
# dmestup info
~~~