Making an online backup of a mounted journaled file system (JFS) or enhanced journaled file system (JFS2) creates a static image of the logical volume that contains the file system. The following procedures describe how to make an online backup. Which procedure you choose depends on whether the file system is a JFS or JFS2.
To make an online backup of a mounted JFS, the logical volume that the file system resides on and the logical volume that its log resides on must be mirrored.
To split off a mirrored copy of the /home/xyz file system to a new mount point named /jfsstaticcopy, type the following:
chfs -a splitcopy=/jfsstaticcopy /home/xyz
You can control which mirrored copy is used as the backup by using the copy attribute. The second mirrored copy is the default if a copy is not specified by the user. For example:
chfs -a splitcopy=/jfsstaticcopy -a copy=1 /home/xyz
At this point, a read-only copy of the file system is available in /jfsstaticcopy. Any changes made to the original file system after the copy is split off are not reflected in the backup copy.
To reintegrate the JFS split image as a mirrored copy at the /testcopy mount point, use the following command:
rmfs /testcopy
The rmfs command removes the file system copy from its split-off state and allows it to be reintegrated as a mirrored copy.
Beginning with AIX 5.2, you can make a snapshot of a mounted JFS2 that establishes a consistent block-level image of the file system at a point in time. The snapshot image remains stable even as the file system that was used to create the snapshot, called the snappedFS, continues to change. The snapshot retains the same security permissions as the snappedFS had when the snapshot was made.
In the following scenario, you create a snapshot and back up the snapshot to removable media without unmounting or quiescing the file system, all with one command: backsnap. You can also use the snapshot for other purposes, such as accessing the files or directories as they existed when the snapshot was taken. You can do the various snapshot procedures using Web-based System Manager, SMIT, or the backsnap and snapshot commands.
To create a snapshot of the /home/abc/test file system and back it up (by name) to the tape device /dev/rmt0, use the following command:
backsnap -m /tmp/snapshot -s size=16M -i f/dev/rmt0 /home/abc/test
This command creates a logical volume of 16 megabytes for the snapshot of the JFS2 file system (/home/abc/test). The snapshot is mounted on /tmp/snapshot and then a backup by name of the snapshot is made to the tape device. After the backup completes, the snapshot remains mounted. Use the -R flag with the backsnap command if you want the snapshot removed when the backup completes.