Snapshot reserve is set as a percentage of the total storage unit size. For example, if the storage unit is 50 GB and you set the snapshot reserve to 10%, the amount of space reserved for snapshots is 5 GB. When the amount of space used by snapshots grows to 5 GB, older snapshots are automatically deleted to make room for new snapshots. If the storage unit size increases to 100 GB, then the snapshot reserve increases to 10 GB. The maximum snapshot reserve you can set is 200%. If your storage unit grows to the maximum size of 128 TB, a 200% snapshot reserve allows you to take 2 complete snapshots.

By default, snapshot reserve is set to 0% and snapshot auto-delete is not enabled.

Beginning with ONTAP 9.18.1, you can modify the default snapshot reserve during or after the creation of storage units and during the creation of consistency groups. You can also modify the default snapshot reserve on existing storage virtual machines (VMs). In ONTAP 9.17.1 and earlier, you cannot modify these settings.

Snapshot reserve is set to the same percentage for all storage units in a consistency group at the time the consistency group is created. Snapshot reserve must be individually set on any storage units added later.