Aggregate Snapshot copy management
An aggregate Snapshot copy is a point-in-time, read-only image of an aggregate. It is similar to a volume Snapshot copy, except that it captures the contents of the entire aggregate, rather than any particular volume. You use aggregate Snapshot copies when the contents of an entire aggregate need to be recorded. However, you do not restore data directly from an aggregate Snapshot copy. To restore data, you use a volume Snapshot copy.
You use aggregate Snapshot copies in the following situations:
- If you are using MetroCluster or RAID SyncMirror and you need to break the mirror, an aggregate Snapshot copy is created automatically before breaking the mirror to decrease the time it takes to resync the mirror later.
- If you are making a global change to your storage system, and you want to be able to restore the entire system state if the change produces unexpected results, you take an aggregate Snapshot copy before making the change.
- If the aggregate file system becomes inconsistent, aggregate Snapshot copies can be used by technical support to restore the file system to a consistent state.
For more information about Snapshot copies, see the Data ONTAP Data Protection Online Backup and Recovery Guide.
- How to create aggregate Snapshot copies
Usually, you do not need to create aggregate Snapshot copies manually. A schedule is automatically set up to generate new aggregate Snapshot copies periodically. In most cases, you should not need to change the aggregate Snapshot copy schedule.
- Aggregate Snapshot reserve
Just as there is space reserved for volume Snapshot copies in their volume (the volume Snapshot reserve), there is space reserved for aggregate Snapshot copies in the aggregate. This space is called the aggregate Snapshot reserve. Usually, the default aggregate Snapshot reserve of 5 percent is sufficient. However, you might increase the aggregate Snapshot reserve under some circumstances.
- Automatic aggregate Snapshot copy deletion
As more and more data blocks in the aggregate are changed, the aggregate Snapshot reserve gradually becomes full. Because aggregate Snapshot copies usually do not need to be preserved for long periods of time (you usually need only the most recent aggregate Snapshot copy), Data ONTAP automatically deletes the oldest aggregate Snapshot copies to recover space in the aggregate Snapshot reserve.
- Disabling automatic aggregate Snapshot copy creation
You can turn off automatic aggregate Snapshot copy creation for a particular aggregate, using the same nosnap option that you would for volume Snapshot copy. Disabling automatic aggregate Snapshot copy creation reclaims the free space used for the aggregate Snapshot reserve. However, you are advised to leave automatic aggregate Snapshot copy creation enabled, in case you need any low-level file system repair.
