Ubuntu - LVM - Reduce the size of an LVM logical volume

To reduce the size of an existing LVM logical volume

Prerequisites

Shrinking a logical volume is likely to destroy any filesystem located on that volume if you do not make appropriate preparations. If you want to preserve existing files then you will need to:

reduce the size of the filesystem by the required amount, then
reduce the size of the underlying block device (the logical volume) to match that of the filesystem.

These instructions cover the second step only. The method for the first step will depend on the type of filesystem. Filesystems that can be shrunk include ext2, ext3, ext4 and reiserfs.

Some filesystems cannot be shrunk, either because their design makes this impracticable or because the necessary software has not been written. In that case your only option is to move the files somewhere else, then recreate the filesystem, then move the files back.

A logical volume can be shrunk using the lvreduce command. You can specify either the amount by which you want to reduce the size of the volume:

lvreduce --size -40G /dev/vg01/foo

or the final size that you want to achieve:

lvreduce --size 80G /dev/vg01/foo

Because of the high potential for data loss, lvreduce asks for confirmation:

  WARNING: Reducing active logical volume to 80.00 GB
  THIS MAY DESTROY YOUR DATA (filesystem etc.)
Do you really want to reduce foo? [y/n]:

If the logical volume contains a filesystem that you wish to preserve then you must not make the volume smaller than the filesystem. This would be a good time to check that you have specified:

the correct volume group and
the correct size (including units).

If you decide to proceed and the operation is successful then you should see a response of the form:

  Reducing logical volume foo to 80.00 GB
  Logical volume foo successfully resized

Testing

Verify the new size of the logical volume using the lvdisplay command:

lvdisplay /dev/vg01/foo

This should give a response of the form:

  --- Logical volume ---
  LV Name                /dev/vg01/foo
  VG Name                vg0
  LV UUID                CbqMvN-g5pj-OF79-GD1e-xmAA-55Tn-Q0McFc
  LV Write Access        read/write
  LV Status              available
  # open                 0
  LV Size                80.00 GB
  Current LE             20480
  Segments               1
  Allocation             inherit
  Read ahead sectors     auto
  - currently set to     256
  Block device           254:100

Troubleshooting

Troubleshooting LVM

Errors

Snapshot origin volumes cannot be reduced in size

The error:

Snapshot origin volumes cannot be reduced in size yet.

indicates that one or more snapshots exist of the logical volume that you are attempting to reduce in size. At the time of writing (as of version 2.02.66) LVM did not support this, so if you want to shrink the volume from which the snapshots were made then you will need to delete the snapshots. You can identify them using the lvs command, looking in the column headed 'Origin'.

Alternatives

lvresize

An alternative to lvreduce is to use the lvresize command:

lvresize --size -40G /dev/vg01/foo

or:

lvresize --size 80G /dev/vg01/foo

The difference is that lvreduce can only reduce the size of a volume, whereas lvresize can increase or reduce it. lvreduce is recommended here because it may catch some errors, but either choice would be reasonable.

Wiki

Table of Contents