How to increase the size of an LVM logical volume

When an application mount runs low on space, adding capacity to the volume group is only part of the storage change. The logical volume and the filesystem mounted from it both need to grow, or df can keep reporting the old size while writes still fail.

LVM extends a logical volume by allocating free extents from its volume group. Running lvextend with --resizefs also asks fsadm to grow the filesystem after the block device changes, which keeps the mounted path and the logical volume in step for supported filesystems.

The volume group must show enough VFree before the grow starts, and a tested backup or recent storage snapshot should cover the mounted data. Use the dedicated root-filesystem procedure for / because boot, rescue, and rollback expectations are different from an ordinary application mount.

1. Identify the mounted filesystem and its backing logical volume.

   $ findmnt /srv/data --output TARGET,SOURCE,FSTYPE,SIZE,AVAIL
   TARGET    SOURCE                  FSTYPE   SIZE  AVAIL
   /srv/data /dev/mapper/vgdata-data ext4   487.2M 451.2M

   Replace /srv/data with the mount point that needs more capacity. The SOURCE column should point to the LVM device that will be extended.

2. Check free space in the volume group.

   $ sudo vgs vgdata
     VG     #PV #LV #SN Attr   VSize  VFree 
     vgdata   1   1   0 wz--n- <2.00g <1.50g

   Replace vgdata with the volume group that contains the logical volume. Add storage to the volume group first when VFree is smaller than the amount being added.

3. Check the current logical volume size.

   $ sudo lvs --options lv_path,lv_size vgdata/data
     Path             LSize  
     /dev/vgdata/data 512.00m

   The path can be written as vgdata/data, /dev/vgdata/data, or /dev/mapper/vgdata-data. Use the same logical volume shown by findmnt.

4. Confirm that a tested backup or recent storage snapshot covers the mounted data.

   ext4 and XFS can grow while mounted in normal conditions, but targeting the wrong logical volume or discovering filesystem damage during the grow can still interrupt the workload.

5. Extend the logical volume and grow the filesystem.

   $ sudo lvextend --resizefs --size +512M /dev/vgdata/data
     File system ext4 found on vgdata/data mounted at /srv/data.
     Size of logical volume vgdata/data changed from 512.00 MiB (128 extents) to 1.00 GiB (256 extents).
     Extending file system ext4 to 1.00 GiB (1073741824 bytes) on vgdata/data...
   resize2fs /dev/vgdata/data
   Filesystem at /dev/vgdata/data is mounted on /srv/data; on-line resizing required
   ##### snipped #####
     Extended file system ext4 on vgdata/data.
     Logical volume vgdata/data successfully resized.

   Replace +512M with the amount to add. Omit --resizefs only when the filesystem will be grown separately after the logical volume change.

6. Verify the larger logical volume size.

   $ sudo lvs --options lv_path,lv_size vgdata/data
     Path             LSize
     /dev/vgdata/data 1.00g

7. Verify the larger mounted filesystem size.

   $ df -h /srv/data
   Filesystem               Size  Used Avail Use% Mounted on
   /dev/mapper/vgdata-data  991M  156K  935M   1% /srv/data

   If df still reports the old size, recheck the filesystem type and grow it manually after confirming that lvs shows the larger logical volume.

8. Check a known file from the mounted path.

   $ cat /srv/data/keep.txt
   archive record

   Use a real application file, database check, or service smoke test for the mounted path in production.