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.
For more information about Snapshot copies, see the Data Protection Online Backup and Recovery Guide.
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:
The commands you use to manage aggregate Snapshot copies are the same as the ones you use to manage volume Snapshot copies, with the -A flag added. However, be sure to read the rest of this section to understand how to manage your 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.
If you do need to create an aggregate Snapshot copy manually, you use the same command as you would for a volume Snapshot copy, except that you add the -A flag. For more information on creating Snapshot copies, see the Data Protection Online Backup and Recovery Guide.
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.
The default size of the aggregate Snapshot reserve is five percent of the aggregate size. For example, if the size of your aggregate is 500 GB, then 25 GB is set aside for aggregate Snapshot copies.
Note
Unlike volume Snapshot copies, aggregate Snapshot copies cannot consume any space outside of their Snapshot reserve.
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.
When an aggregate Snapshot copy is automatically deleted, a message similar to this one is logged:
Sun May 23 15:10:16 EST [wafl.snap.autoDelete:info]: Deleting snapshot `nightly.0' in aggregate `aggr1' to recover storage
Usually, the default aggregate Snapshot reserve of five percent is sufficient. However, if you find that aggregate Snapshot copies are being created and deleted often enough to affect system performance, then you should increase the aggregate Snapshot reserve.
Note
If you have automatic aggregate Snapshot copy creation enabled, you should not decrease the size of the aggregate Snapshot reserve below the default of five percent. If you need to reclaim the space being used for the aggregate Snapshot reserve, disable automatic aggregate Snapshot copy creation using the procedure outlined in About disabling automatic aggregate Snapshot copy creation.
In most cases you should leave automatic aggregate Snapshot copy deletion enabled. If this option is turned off for a particular aggregate, then every volume in that aggregate requires up to two times its size in order to satisfy a space guarantee of volume.
However, in some specific situations, you may need to disable automatic aggregate Snapshot copy deletion temporarily. For example, if you want to create an aggregate Snapshot copy before breaking your RAID SyncMirror, you would want to make sure that Snapshot copy is not automatically deleted. To disable automatic aggregate Snapshot copy deletion, you use the aggregate option command.
For example, to turn off automatic aggregate Snapshot copy deletion for the aggregate myAggr, you would use the following command:
aggr options myAggr snapshot_autodelete off
Note
If you do not have sufficient free space in your aggregate to satisfy the new space requirements when you turn off automatic aggregate Snapshot copy deletion, then space guarantees will be disabled for one or more of your volumes. For this reason, you should plan to re-enable automatic aggregate Snapshot copy deletion as quickly as possible.
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. However, you are advised to leave automatic aggregate Snapshot copy creation enabled, in case you need any low-level file system repair.
Attention
Do not disable automatic aggregate Snapshot copy creation if you have a MetroCluster configuration, or if you are using RAID SyncMirror. Aggregate Snapshot copies are required for those configurations for correct system operation.
To disable automatic aggregate Snapshot copy creation, and reclaim the free space being used for the aggregate Snapshot reserve, complete the following steps.
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Last updated: 21-Dec-2005 09:03:29