Starting from AIX V6.1 IBM offers the ability to create snapshots with the file system. This is called as “JFS2 Internal Snapshot”. These internal snapshots are stored under /fsmountpoint/.snapshot/snapshotname.
Both the internal and the external snapshots keep track of the changes to the snapped file system by saving the modified or deleted file blocks. Snapshots provide point-in-time (PIT) images of the source file system. Basically snapshots are used for taking PIT images (backup) of a file system during production runtime.
Advantages of Internal Snapshot:
a) No super user permissions are necessary to access data from a snapshot, since no initial mount operation is required.
b) No additional file system or logical volume needs to be maintained and monitored.
c) Snapshots are easily NFS exported, since they are in held in the same filesystem.
Management of Internal snapshots:
A JFS2 file system must be created with the new -a isnapshot=yes option. Existing file systems created without the isnapshot option cannot be used for internal snapshots. They have to be recreated or have to use external snapshots.
To create an internal snapshot:
# snapshot -o snapfrom=/oracle -n snap10
Snapshot "snap10" for file system /oracle created.
To create an external snapshot:
# snapshot -o snapfrom=/oralce /dev/snaporacle
This command creates a snapshot for the /oracle file system on the /dev/snaporacle logical volume, which already exists.
To list all snapshots for a file system:
# snapshot –q /oracle
Snapshots for /oracle
Current Name Time
* snap10 Mon Dec 15 09:17:51 CDT 2008
Files under this snapshot “snap10” are available under /oracle/.snapshot/snap10 directory. These files are read only; no modifications are allowed.
To delete an internal snapshot:
# snapshot –d –n snap10 /oracle
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