The snap list command shows the amount of disk space consumed by snapshots in a specified volume. This command enables you to see how much disk space each snapshot uses and helps you determine an appropriate snapshot reserve. The snap list command also shows whether a snapshot is currently being used for backup and whether it is needed for a restartable dump or another backup application.
To display the snapshot statistics for a volume, complete the following step.
| 1 | Enter the following command line: snap list volume_name volume_name is the name of the volume for which you want statistics. |
Following is an example of the snap list command output. If you do not specify a volume name in the command, the output contains statistics about each volume in the system.
filerA> snap list vol0
Volume vol0
%/used %/total date name
---------- ---------- ------------ --------
0% ( 0%) 0% ( 0%) Jan 19 08:01 hourly.0
1% ( 1%) 1% ( 1%) Jan 19 00:01 nightly.0
2% ( 2%) 2% ( 2%) Jan 18 20:01 hourly.1
3% ( 2%) 2% ( 2%) Jan 18 16:01 hourly.2
3% ( 2%) 3% ( 2%) Jan 18 12:01 hourly.3
5% ( 3%) 4% ( 3%) Jan 18 00:01 nightly.1
7% ( 4%) 6% ( 4%) Jan 17 00:00 nightly.2
8% ( 4%) 7% ( 4%) Jan 16 00:01 nightly.3
10%( 5%) 9% ( 4%) Jan 15 00:01 nightly.4
The %/used column shows space consumed by snapshots as a percentage of disk space being used in the volume. The first number is cumulative for all snapshots listed so far, and the second number is for the specified snapshot alone.
The %/total column shows space consumed by snapshots as a percentage of total disk space (both space used and space available) in the volume.
Cumulative snapshot space is the total space used by this snapshot and all other more recent snapshots (the ones preceding this snapshot in the snap list output).
The %/used number is the most useful for planning the snapshot reserve because it is more likely to remain constant as the file system fills.
The information in Sample snap list command output shows a volume that keeps five nightly snapshots and four hourly snapshots.
The sample output shows that the overhead for snapshots is only 10%, so the default snapshot reserve of 20% seems to be a waste of disk space. Assuming that this pattern of change holds, a reserve of 12% to 15% provides a safe margin to ensure that deleting files frees disk space when the active file system is full. For information about the snapshot reserve, see Understanding the snapshot reserve.
The values in parentheses, which show the space used by an individual snapshot, are useful in identifying a particular snapshot to delete when the file system is full. However, deleting a particular snapshot does not necessarily release the amount of disk space indicated, because other snapshots might be referring to the same blocks.
If you do not want the amount of disk space consumed by all snapshots to exceed a certain percentage of the used disk space, use the cumulative values in the snap list output to determine which snapshots to delete. In the preceding example, if you do not want more than 5% of used disk space to be spent by snapshots, delete all snapshots listed below nightly.1 in the snap list output; that is, nightly.2, nightly.3, and nightly.4. After deleting the snapshots, nightly.1 and all the other more recent snapshots consume 5% of the used disk space.
The snap list command displays the notation "busy" after the name of a snapshot if the snapshot is being actively used by an application, as shown the example below for the snapshot hourly.0. Busy snapshots cannot be deleted.
snap list vol0
Volume vol0
%/used %/total date name
-------- ------ ------------ --------
0% ( 0%) 0% ( 0%) Jan 19 08:01 hourly.0 (busy)
1% ( 1%) 1% ( 1%) Jan 19 00:01 nightly.0(snapmirror)
2% ( 2%) 2% ( 2%) Jan 18 20:01 hourly.1 (busy,snapmirror)
3% ( 2%) 2% ( 2%) Jan 18 16:01 hourly.2
3% ( 2%) 3% ( 2%) Jan 18 12:01 hourly.3
5% ( 3%) 4% ( 3%) Jan 18 00:01 nightly.1 (backup[9])
7% ( 4%) 6% ( 4%) Jan 17 00:00 nightly.2
8% ( 4%) 7% ( 4%) Jan 16 00:01 nightly.3
10%( 5%) 9% ( 4%) Jan 15 00:01 nightly.4
The snap list command also displays the name of an application next to a snapshot name if the application needs the snapshot currently or at a later time. For example, "backup" is displayed next to the snapshot name to show that the snapshot is the result of a dump command transfer that was interrupted but is restartable. The number following "backup" is the backup ID assigned by the backup status command. The notation "snapmirror" next to the snapshot name means that SnapMirror is retaining the snapshot to maintain a source-destination relationship.
If you restore files with the snap restore command, and then issue the snap list command, the snap list command can take up to several minutes to complete. This condition persists until the snapshot from which you restored the file is purged from the system after reaching the end of its normal snapshot retention cycle.
For more information see Reverting a file to a selected snapshot.
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Part No. 210-00476
File: snap10.htm
Last updated: 11/13/03 17:17:21