Installation guide

Shrinking Logical Volumes

[root@taft-03 ~]# lvs -a -o +devices

LV VG Attr LSize Log Copy% Devices

mirror taft Mwi-a- 200.00g mirror_mlog 50.16

mirror_mimage_0(0),mirror_mimage_1(0)

[mirror_mimage_0] taft Iwi-ao 200.00g /dev/sdb1(0)

[mirror_mimage_0] taft Iwi-ao 200.00g /dev/sdg1(0)

[mirror_mimage_1] taft Iwi-ao 200.00g /dev/sdc1(0)

[mirror_mimage_1] taft Iwi-ao 200.00g /dev/sdd1(0)

[mirror_mlog] taft lwi-ao 4.00m /dev/sdh1(0)

4.4.13. Shrinking Logical Volumes

To reduce the size of a logical volume, first unmount the file system. You can then use the lvreduce

command to shrink the volume. After shrinking the volume, remount the file system.

Warning

It is important to reduce the size of the file system or whatever is residing in the volume before

shrinking the volume itself, otherwise you risk losing data.

Shrinking a logical volume frees some of the volume group to be allocated to other logical volumes in

the volume group.

The following example reduces the size of logical volume lvol1 in volume group vg00 by 3 logical

extents.

# lvreduce -l -3 vg00/lvol1

4.5. Controlling LVM Device Scans with Filters

At startup, the vgscan command is run to scan the block devices on the system looking for LVM

labels, to determine which of them are physical volumes and to read the metadata and build up a

list of volume groups. The names of the physical volumes are stored in the cache file of each node

in the system, /etc/lvm/cache/.cache. Subsequent commands may read that file to avoiding

rescanning.

You can control which devices LVM scans by setting up filters in the lvm.conf configuration file. The

filters in the lvm.conf file consist of a series of simple regular expressions that get applied to the

device names that are in the /dev directory to decide whether to accept or reject each block device

found.

The following examples show the use of filters to control which devices LVM scans. Note that some of

these examples do not necessarily represent best practice, as the regular expressions are matched

freely against the complete pathname. For example, a/loop/ is equivalent to a/.*loop.*/ and

would match /dev/solooperation/lvol1.

The following filter adds all discovered devices, which is the default behavior as there is no filter

configured in the configuration file: