The snap list command shows the amount of disk space consumed by Snapshot copies in a specified volume. This command enables you to see how much disk space each Snapshot copy uses and helps you determine an appropriate Snapshot reserve. The snap list command also shows whether a Snapshot copy 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 |
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.
systemA> 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 Snapshot copies as a percentage of disk space being used in the volume. The first number is cumulative for all Snapshot copies listed so far, and the second number is for the specified Snapshot copy alone.
The %/total column shows space consumed by Snapshot copies 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 copy and all other more recent Snapshot copies (the ones preceding this Snapshot copy 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 Snapshot copies and four hourly Snapshot copies.
The sample output shows that the overhead for Snapshot copies 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 copy, are useful in identifying a particular Snapshot copy to delete when the file system is full. However, deleting a particular Snapshot copy does not necessarily release the amount of disk space indicated, because other Snapshot copies might be referring to the same blocks.
If you do not want the amount of disk space consumed by all Snapshot copies to exceed a certain percentage of the used disk space, use the cumulative values in the snap list output to determine which Snapshot copies to delete. In the preceding example, if you do not want more than 5% of used disk space to be spent by Snapshot copies, delete all Snapshot copies listed below nightly.1 in the snap list output; that is, nightly.2, nightly.3, and nightly.4. After deleting the Snapshot copies, nightly.1 and all the other more recent Snapshot copies consume 5% of the used disk space.
The snap list command displays the notation "busy" after the name of a Snapshot copy if the Snapshot copy is being actively used by an application, as shown the example below for the Snapshot copy hourly.0. Busy Snapshot copies 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 copy name if the application needs the Snapshot copy currently or at a later time. For example, "backup" is displayed next to the Snapshot copy name to show that the Snapshot copy 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 copy name means that SnapMirror is retaining the Snapshot copy to maintain a source-destination relationship.
Note
Ownership information for a busy Snapshot copy is useful for determining whether to stop the activity in progress. For example, if the snap list command output displays a locked Snapshot copy that is imposing a resource constraint, you can delete that Snapshot copy and free up space.
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 copy 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 copy.
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Part No. 210-01081_B0
File: snap10.htm
Last updated: 01-Dec-2005 16:35:59