Troubleshooting Filesystem Capacity Shrinking

If the capacity of a ZFS dataset appears to shrink or reduce in size, the most likely reason is because the “missing” space is consumed by ZFS Boot Environments or ZFS snapshots created by the user manually.

ZFS Boot Environments/Snapshots consume space based on how different the current disk contents are compared to when the snapshot was taken. Rather than appear as filesystem usage like a traditional file, the apparent capacity of the filesystem is reduced instead. This allows traditional filesystem utilities to accurately account for space used by actual files vs filesystem data which is fundamentally different.


On systems with ZFS Boot Environments, use the ZFS Dashboard Widget to see the ZFS pool size as a total, rather than the size and consumption of individual filesystems.

Cleaning up older ZFS Boot Environments/snapshots will return the space they consumed and the capacity of the filesystem will increase accordingly.

The ZFS Boot Environment list in the GUI displays a total amount of usage but it is possible to see a more detailed breakdown of usage with the zfs list -t snapshot command in the CLI:

: zfs list -t snapshot
NAME                                                       USED  AVAIL  REFER  MOUNTPOINT
pfSense/ROOT/default@2023-03-27-13:48:48-0                 991M      -  1.21G  -
pfSense/ROOT/default@2023-05-15-10:36:04-0                 724M      -  1.29G  -
pfSense/ROOT/default@2023-05-16-09:38:51-0                 715M      -  1.29G  -
pfSense/ROOT/default@2023-05-19-08:44:32-0                 715M      -  1.29G  -
pfSense/ROOT/default@2023-05-22-07:59:47-0                 720M      -  1.30G  -
pfSense/ROOT/default/cf@2023-02-20-12:39:12-0             2.82M      -  2.88M  -
pfSense/ROOT/default/cf@2023-03-27-13:48:48-0             2.59M      -  2.65M  -
pfSense/ROOT/default/cf@2023-05-15-10:36:04-0             1.16M      -  2.90M  -
pfSense/ROOT/default/cf@2023-05-16-09:38:51-0              216K      -  2.90M  -
pfSense/ROOT/default/cf@2023-05-19-08:44:32-0              216K      -  2.89M  -
pfSense/ROOT/default/cf@2023-05-22-07:59:47-0             1.25M      -  2.89M  -
pfSense/ROOT/default/var_cache_pkg@2023-02-20-12:39:12-0   216M      -   216M  -
pfSense/ROOT/default/var_cache_pkg@2023-03-27-13:48:48-0   174M      -   174M  -
pfSense/ROOT/default/var_cache_pkg@2023-05-15-10:36:04-0   184M      -   193M  -
pfSense/ROOT/default/var_cache_pkg@2023-05-16-09:38:51-0   184M      -   198M  -
pfSense/ROOT/default/var_cache_pkg@2023-05-19-08:44:32-0   184M      -   199M  -
pfSense/ROOT/default/var_cache_pkg@2023-05-22-07:59:47-0   185M      -   200M  -
pfSense/ROOT/default/var_db_pkg@2023-02-20-12:39:12-0     5.61M      -  6.81M  -
pfSense/ROOT/default/var_db_pkg@2023-03-27-13:48:48-0     3.25M      -  6.95M  -
pfSense/ROOT/default/var_db_pkg@2023-05-15-10:36:04-0     2.39M      -  7.04M  -
pfSense/ROOT/default/var_db_pkg@2023-05-16-09:38:51-0     2.38M      -  7.04M  -
pfSense/ROOT/default/var_db_pkg@2023-05-19-08:44:32-0     2.52M      -  7.04M  -
pfSense/ROOT/default/var_db_pkg@2023-05-22-07:59:47-0     2.89M      -  7.06M  -