Dell EqualLogic PS6210XS EqualLogic Group Manager Administrator s Guide PS Ser - Page 235

About Snapshot Space Borrowing Snapshot space borrowing enables the system to temporarily increase the available snapshot space for a volume by borrowing from other sources. If borrowed space is needed for other functions, the firmware might delete snapshots that are borrowing space. Because of this potential deletion, you should always be aware of when snapshots are borrowing space. NOTE: Borrowed space is intended to help during peaks of activity when more space is needed temporarily. It does not take the place of carefully provisioning snapshot reserves. A regular (standard) volume has a fixed volume reserve; this volume reserve for regular volumes does not change when its usage increases. With a thin-provisioned volume, the system automatically increases volume reserve as more data is written to that volume. As the volume reserve increases, so does the allotted snapshot space for that volume. Snapshot borrowing allows a thin-provisioned volume to keep its snapshots when snapshot reserve shrinks due to volume unmapping. When a volume is unmapped, the volume reserve shrinks; because snapshot reserve is a percentage of volume reserve, snapshot reserve also shrinks. Activate Snapshot Space Borrowing NOTE: • If you are using snapshot space borrowing on a new group in which all the members are running the latest version of the Group Manager software, snapshot borrowing is available immediately. • If you are upgrading the members in the group from a previous version of the firmware, the Disallow Downgrades function must be set on each member in the group before snapshot borrowing can be activated. This function is set automatically when all members in the group are running Group Manager firmware version 6.0 or later. • All members in the group must be running Group Manager firmware version 6.0 or later. Snapshot space borrowing does not work in environments running mixed versions of the firmware. • You can set a system default policy for new volumes. For existing volumes, you must configure the settings on each individual volume. To set a system default policy for snapshot borrowing for new volumes: 1. Click Group → Group Configuration. 2. Click the Defaults tab. 3. In the Snapshot space reserve section, specify a value (in percent) for the snapshot reserve (the default value is 100 percent, but it can exceed 100). 4. In the Volume Settings panel, navigate to the Snapshot space recovery section. 5. Select Delete oldest snapshot, if it has not already been selected. This option enables snapshot space borrowing; it will not work without this option selected. 6. Make sure that the Borrow snapshot space as needed checkbox is selected. When snapshot borrowing is enabled, the snapshot in-use space is allowed to exceed the snapshot reserve space. Some warning messages about snapshot reserve in-use space on the volume are suppressed when snapshot space borrowing is in effect; however, warning messages are still issued when in-use snapshot space exceeds the warning threshold. NOTE: Snapshot space borrowing cannot be enabled if the Set volume offline option is selected under Snapshot space recovery. If you disable the system default policy for snapshot space borrowing for a newly created volume, existing volumes will still have snapshot space borrowing enabled. Control Snapshot Space Borrowing You can control whether or not a volume is allowed to borrow space for snapshots. Snapshot space borrowing enables you to temporarily increase the available snapshot space for a volume by borrowing space from other sources. Borrowing can help prevent the oldest snapshots from potentially being deleted when the volume's allocated snapshot reserve is depleted. To control snapshot space borrowing for existing volumes: About Backing Up and Protecting Your Data 235