You can use the snap list command to view the disk space utilization by Snapshot copies. This information helps you determine an appropriate Snapshot copy reserve. The snap list command also shows whether a Snapshot copy is required for a replication operation, such as SnapMirror.
Step
1. To display the Snapshot copy statistics for a volume, enter the following command:
snap list vol_name
vol_name is the name of the volume for which you want statistics.
If you do not specify a volume name in the command, the output contains statistics about each volume in the system.
Example
The following example gives a sample output of the snap list command:
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
How the snap list output is calculated
The snap list output is calculated in a number of ways.
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 first number is equal to
cumulative Snapshot copy space
cumulative Snapshot copy space + file system space 100% x
• The second number is equal to
this Snapshot copy
this Snapshot copy + file system space 100% x
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.
• The first number is equal to
cumulative Snapshot copy space total disk space in this volume 100% x
Cumulative Snapshot copy 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 second number is equal to
this Snapshot copy
total disk space in this volume 100% x
Summary of the snap list command output: The %/used number is useful for planning the Snapshot copy reserve because it is more likely to remain constant as the file system fills.
The information 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 percent, so the default Snapshot copy reserve of 20 percent seems to be a waste of disk space. If this pattern of change holds, a reserve of 12 percent to 15 percent provides a safe margin to ensure that deleting files frees disk space when the active file system is full.
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.
Related concepts
What the Snapshot copy reserve is on page 48
How to use cumulative Snapshot copy values
If you want the amount of disk space consumed by all Snapshot copies not to exceed a certain percentage of the used disk space, you can use the cumulative values in the snap list command output to determine which Snapshot copies to delete.
For example, if you do not want more than 5 percent of used disk space to be spent by Snapshot copies, you can 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 percent of the used disk space.
Displaying Snapshot copy use and dependencies
The output of the snap list command shows whether a Snapshot copy is being actively used by an application or a replication operation.
Step
1. To view the list of Snapshot copies, enter the following command:
snap list vol_name Example
A sample output is given in the following example:
systemA> snap list vol1 Volume vol1
%/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 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.
snap list performance after a snap restore file operation
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.
Related tasks
Reverting a file to a selected Snapshot copy on page 69