Making an online backup of a mounted JFS file system creates a snapshot of the logical volume that contains the file system. This procedure describes how to split off a mirrored copy to be used to make a backup.
In order to make an online backup of a mounted file system, the logical volume that the file system resides on must be mirrored. The JFS log logical volume for the file system must also be mirrored.
NOTE: Because the file writes are asynchronous, the snapshot might not contain all data that was written immediately before the snapshot is taken. Modifications that start after the snapshot begins might not be present in the backup copy. Therefore, it is recommended that file system activity be minimal while the split is taking place.
The user can control which copy is used as the backup by using the copy attribute. The second copy is the default if a copy is not specified by the user.
The following example shows a copy of the file system /testfs split off. The example assumes that there are two copies of the file system.
chfs -a splitcopy=/backup -a copy=2 /testfs
Once this command completes successfully, a copy of the file system is available read-only in /backup.
Note that additional changes made to the original file system after the copy is split off are not reflected in the backup copy.
rmfs /backup
The rmfs command removes the file system copy from its split off state and allows it to be reintegrated as a mirrored copy.
For additional information about mirrored logical volumes, see the Logical Volume Storage Overviewin AIX 5L Version 5.1 System Management Concepts: Operating System and Devices, or the mklv and mklvcopy commands.