Situation where you need to shrink lvm partition or file system are rare due to the plenty of storage space we have nowadays, but first let’s clarify one thing, the correct term is this : some time we need to shrink, reduce or resize an LV (logical volume) file system, which can be an ext3, ext4 or other.
So here is the actual scenario: We have two PV (Physical volume) grouped into one VG (volume group), on this volume group, an LV was created to host a small mysql database.
The database size represent, for example 1% of the total available space, and the database administrator estimated that it will not grow for no more than 25% per year, which in our case, is a total waste of resource.
Here is the actual configuration of the LVM, volume group and the physical volume:
Physical volume
[root@host581 ~]# pvs PV VG Fmt Attr PSize PFree /dev/sda2 VolGroup lvm2 a-- 7.51g 0 /dev/sdc vgdata lvm2 a-- 100.00m 0 /dev/sdd vgdata lvm2 a-- 100.00m 0
Volume group
[root@host581 ~]# vgs VG #PV #LV #SN Attr VSize VFree VolGroup 1 2 0 wz--n- 7.51g 0 vgdata 2 1 0 wz--n- 200.00m 0
Used space:
[root@host581 ~]# df -h /data
Filesystem Size Used Avail Use% Mounted on
/dev/mapper/vgdata-lv_mysql
194M 26M 159M 14% /data
As we can see the logical volume is oversized for this database, so let’s shrink lvm partition /dev/mapper/vgdata-lv_mysql, or file system if you prefer:
1- First unmount the file system
[root@host581 ~]# umount /data [root@host581 ~]#
2- Check the file system for any errors or inconsistency:
[root@host581 ~]# e2fsck -f /dev/mapper/vgdata-lv_mysql e2fsck 1.41.12 (17-May-2010) 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/mapper/vgdata-lv_mysql: 12/51200 files (0.0% non-contiguous), 32110/204800 blocks
3- Resize the file system
[root@host581 ~]# resize2fs -p /dev/mapper/vgdata-lv_mysql 100m resize2fs 1.41.12 (17-May-2010) Resizing the filesystem on /dev/mapper/vgdata-lv_mysql to 102400 (1k) blocks. Begin pass 3 (max = 25) Scanning inode table XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX The filesystem on /dev/mapper/vgdata-lv_mysql is now 102400 blocks long.
4- Reduce the lvm partition size
[root@host581 ~]# lvreduce -L 100M /dev/mapper/vgdata-lv_mysql WARNING: Reducing active logical volume to 100.00 MiB THIS MAY DESTROY YOUR DATA (filesystem etc.) Do you really want to reduce lv_mysql? [y/n]: y Reducing logical volume lv_mysql to 100.00 MiB Logical volume lv_mysql successfully resized
5- Mount the file system
[root@host581 ~]# mount /dev/mapper/vgdata-lv_mysql /data
[root@host581 ~]# df -h
Filesystem Size Used Avail Use% Mounted on
/dev/mapper/VolGroup-lv_root
6.5G 721M 5.5G 12% /
tmpfs 246M 0 246M 0% /dev/shm
/dev/sda1 485M 31M 429M 7% /boot
/dev/mapper/vgdata-lv_mysql
97M 26M 67M 28% /data
We need then to move any physical extent to the disk that we want to keep, this suppose that we have a volume group with the default allocation policy, as shown here on Attr column (letter n), which mean normal:
[root@host581 ~]# vgs VG #PV #LV #SN Attr VSize VFree VolGroup 1 2 0 wz--n- 7.51g 0 vgdata 2 1 0 wz--n- 200.00m 100.00m
The attributes also control the behaviour of our logical volume partition, which can be seen here with the “i” in the attributes which mean inherit from our VG:
[root@host581 ~]# lvs LV VG Attr LSize Origin Snap% Move Log Copy% Convert lv_root VolGroup -wi-ao 6.54g lv_swap VolGroup -wi-ao 992.00m lv_mysql vgdata -wi-ao 100.00m
These allocation policy control how data is distributed between your physical volume.
6- Move any physical extents to the disk that we want to keep.
[root@host581 ~]# pvmove -v /dev/sdd /dev/sdc
7- Reduce the volume group to only contain one physical disk
[root@host581 ~]# vgreduce -v vgdata /dev/sdd
Finding volume group "vgdata"
Using physical volume(s) on command line
Archiving volume group "vgdata" metadata (seqno 3).
Removing "/dev/sdd" from volume group "vgdata"
Creating volume group backup "/etc/lvm/backup/vgdata" (seqno 4).
Removed "/dev/sdd" from volume group "vgdata"
8- Retire the disk from the machine and remove any reference to it, you can have small variation on the disk name if you want to shrink lvm partition based on LUN not local disk.
[root@host581 ]# pvremove /dev/sdd Labels on physical volume "/dev/sdd" successfully wiped
[root@host581 ]# rm -r /dev/sdd [root@host581 ]# ls -l /dev/disk//by-path/pci-0000\:00\:0* lrwxrwxrwx. 1 root root 9 Feb 3 05:16 /dev/disk//by-path/pci-0000:00:01.1-scsi-0:0:0:0 -> ../../sr0 lrwxrwxrwx. 1 root root 9 Feb 3 05:16 /dev/disk//by-path/pci-0000:00:0d.0-scsi-0:0:0:0 -> ../../sda lrwxrwxrwx. 1 root root 10 Feb 3 05:16 /dev/disk//by-path/pci-0000:00:0d.0-scsi-0:0:0:0-part1 -> ../../sda1 lrwxrwxrwx. 1 root root 10 Feb 3 05:16 /dev/disk//by-path/pci-0000:00:0d.0-scsi-0:0:0:0-part2 -> ../../sda2 lrwxrwxrwx. 1 root root 9 Feb 3 05:16 /dev/disk//by-path/pci-0000:00:0d.0-scsi-1:0:0:0 -> ../../sdb lrwxrwxrwx. 1 root root 9 Feb 3 09:44 /dev/disk//by-path/pci-0000:00:0d.0-scsi-2:0:0:0 -> ../../sdc lrwxrwxrwx. 1 root root 9 Feb 3 10:16 /dev/disk//by-path/pci-0000:00:0d.0-scsi-3:0:0:0 -> ../../sdd [root@host581 ]# rm -r /dev/disk//by-path/pci-0000:00:0d.0-scsi-3:0:0:0
9- Remove the device from the SCSI subsystem
[root@host581 ]# echo 1 > /sys/block/sdd/device/delete
If we examine the output from dmesg, we can see that ths disk was removed:
.... sd 5:0:0:0: [sdd] Synchronizing SCSI cache sd 5:0:0:0: [sdd] Stopping disk ....
Our lvm partition is reduced to only one disk, and the file system reflect this as shown here
As a best practice, if you need to shrink lvm partition or file system, be sure to have a backup of your data before, not matter how confident you are with your skills.
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Very helpful, thanks for sharing.
I was looking for a way to shrink my lvm but the majority of tutorials doesn’t involve retiring a physical volume.