Dell EqualLogic PS6210XS EqualLogic Group Manager Administrator s Guide PS Ser - Page 227

NOTE: Generally, snapshots will not be deleted unless you take action to delete them. In some instances, however, snapshots can be deleted by the system. For example, when a new snapshot is taken and not enough snapshot reserve space is available for the new snapshot and the previous one, the older one will be deleted. About Snapshot Reserve Before you can create snapshots of a volume, you must allocate snapshot reserve for the volume. Snapshot reserve is consumed from the pool where the volume resides. You can allocate snapshot reserve when you create a volume, or you can modify a volume's properties to change the snapshot reserve. Snapshot reserve is a percentage of the volume reserve. Because the volume reserve for a thin-provisioned volume changes as volume usage increases, the snapshot reserve for a thin-provisioned volume also changes. The group generates event messages when the amount of free snapshot reserve falls below a user-defined threshold. NOTE: • Depending on the policy that you set for snapshot space recovery, the group preserves snapshot reserve. • Enabling data reduction permanently removes the snapshot reserve functionality from the NAS container. Snapshot Reserve Settings The following snapshot reserve settings use groupwide default values, unless you explicitly change them for a volume: • Snapshot reserve Amount of space, based on a percentage of the volume reserve, that the group allocates to snapshots. When you create a volume, you can specify the snapshot reserve percentage for the volume. Otherwise, the group applies the groupwide default value. You can modify the snapshot reserve value as needed in Group Manager → Group Configuration , under the Default tab. • Snapshot space recovery policy Action the group takes when a new snapshot exceeds snapshot reserve: - Delete the oldest snapshots to free space for new snapshots - Set the volume (and snapshots) offline - Borrow snapshot space as needed You can modify the snapshot space recovery policy in Group Manager → Group Configuration , under the Default tab. If a snapshot has active iSCSI connections, the group closes the connections before deleting the snapshot. NOTE: In some cases, you might want to preserve the data in a snapshot that could be at risk of deletion. To preserve the data in a snapshot, you can clone the snapshot. • Snapshot space warning percentage Percentage of the snapshot reserve that, when reached by in-use snapshot reserve, results in an event message. The default is 90 percent of the snapshot reserve. For example, if snapshot reserve space is 200MB and the warning level is 90 percent, a warning occurs when in-use snapshot reserve equals or exceeds 180MB. Modify Snapshot Space Reserve Settings If you change the snapshot space reserve, the values in the Pool Space table change. If the new snapshot space reserve value exceeds the capacity of the pool, the free pool space cell displays a negative value. To modify the snapshot space reserve settings for a volume: 1. Click Volumes. 2. Expand Volumes and then select the volume name. 3. In the Activities panel, click Modify settings. About Backing Up and Protecting Your Data 227