2014
Resize root LVM partition
I like to use LVM on my personal laptop to avoid the crazy partition sizing step. When I set up my system I just create some main partitions (swap, / and /home) then I grow them as I need more space.
Lately I installed docker and instead of creating a logical volume for docker data in /var/data/docker I lazily growed my / partition. In fact, at the time I knew it was a mistake. Few weeks later I got sick of it.
Here is how to resize an unmountable parition, e.g. your system root partition.
- create a snapshot SNAP_ROOT of volume ROOT
- shrink the filesystem on SNAP_ROOT
- ask LVM to merge SNAP_ROOT to ROOT, ie. replace the volume with the original filesystem by the shrinked one
- reboot so LVM can do the merge
- reduce ROOT volume size with option
--resizefs
⚠ First you should remount the partition in read-only mode. I wasn’t able to do it because of all the stuff running and I decided to take the risk to continue. If you do so, you’re responsible.
the short way
lvcreate -s ssd/root -L 40G -n root_backup
e2fsck -f /dev/mapper/ssd-root_backup \
&& resize2fs -p -M /dev/mapper/ssd-root_backup
lvconvert --merge ssd/root_backup
reboot
lvresize -L 20G -r ssd/root
the long way
1. create a snapshot SNAP_ROOT
Create a snapshot of the partition, I used a size of 40G (same size of the original partition) but a such value shouldn’t be necessary.
lvcreate -s ssd/root -L 40G -n root_backup
Running lvdisplay shows the original volume and its snapshot. We can see:
- original volume size is 40GB
- snapshot as Copy-On-Write-table size of 40GiB
- 0% of the COW-table is used for now
lvdisplay ssd/root ssd/root_backup
--- Logical volume ---
LV Path /dev/ssd/root
LV Name root
VG Name ssd
…
LV snapshot status source of
root_backup [active]
…
LV Size 40,00 GiB
…
--- Logical volume ---
LV Path /dev/ssd/root_backup
LV Name root_backup
VG Name ssd
…
LV snapshot status active destination for root
LV Status available
…
COW-table size 40,00 GiB
COW-table LE 10240
Allocated to snapshot 0,00%
…
2. shrink the filesystem on SNAP_ROOT
Firstly, a filesystem check must be forced:
e2fsck -f /dev/mapper/ssd-root_backup
e2fsck 1.42.12 (29-Aug-2014)
Passe 1 : vérification des i-noeuds, des blocs et des tailles
Passe 2 : vérification de la structure des répertoires
Passe 3 : vérification de la connectivité des répertoires
Passe 4 : vérification des compteurs de référence
Passe 5 : vérification de l'information du sommaire de groupe
root : 290516/2621440 fichiers (0.2% non contigüs), 4227390/10485760 blocs
Then we are able to resize it:
resize2fs -p -M /dev/mapper/ssd-root_backup
resize2fs 1.42.12 (29-Aug-2014)
En train de redimensionner le système de fichiers sur /dev/mapper/ssd-root_backup à 4527614 (4k) blocs.
The filesystem on /dev/mapper/ssd-root_backup is now 4527614 (4k) blocks long.
Shrinking the filesystem may cause a lot of changes to the volume. During this operation the allocated space of the COW-table will increase.
We can run lvdisplay to observe how many space the resize operation taken from the snapshot COW-table.
lvdisplay ssd/root_backup
--- Logical volume ---
LV Path /dev/ssd/root_backup
LV Name root_backup
...
Allocated to snapshot 17,13%
...
3. merge SNAP_ROOT to ROOT
lvconvert --merge ssd/root_backup
Logical volume ssd/root contains a filesystem in use.
Can't merge over open origin volume.
Merging of snapshot ssd/root_backup will occur on next activation of ssd/root.
4. reboot
LVM can’t merge a snapshot to an active partition: the partition has te be deactivated. This is done by rebooting the system.
reboot
5. reduce ROOT volume
Let’s see the new partition size we have:
df -h
Sys. de fichiers Taille Utilisé Dispo Uti% Monté sur
/dev/mapper/ssd-root 17G 16G 742M 96% /
lvdisplay ssd/root
--- Logical volume ---
LV Path /dev/ssd/root
LV Name root
VG Name ssd
…
LV Size 40,00 GiB
The filesystem has a size of 17G, but the volume size is always 40G. We must use lvm to resize the volume. We use option -r/--resizefs which tell LVM to resize the underlying filesystem to the new size of the volume.
lvresize -L 20G -r ssd/root
resize2fs 1.42.12 (29-Aug-2014)
Le système de fichiers de /dev/mapper/ssd-root est monté sur / ; le changement de taille doit être effectué en ligne
old_desc_blocks = 2, new_desc_blocks = 2
The filesystem on /dev/mapper/ssd-root is now 5242880 (4k) blocks long.
Size of logical volume ssd/root changed from 40,00 GiB (10240 extents) to 20,00 GiB (5120 extents).
Logical volume root successfully resized
Now our partition and our volume size are reduced:
df -h
Sys. de fichiers Taille Utilisé Dispo Uti% Monté sur
/dev/mapper/ssd-root 20G 16G 3,4G 83% /
lvdisplay ssd/root
--- Logical volume ---
LV Path /dev/ssd/root
LV Name root
VG Name ssd
…
LV Size 20,00 GiB