Consider defining a management class specifically for logical volume backups. To enable clients to restore a logical volume and then reconcile the results of any file backup operations since the logical volume backup was made, you must set up management classes with the backup copy group set up differently from the STANDARD.
The Versions Data Exists, Versions Data Deleted, and Retain Extra Versions parameters work together to determine over what time period a client can restore a logical volume image and reconcile later file backups. Also, you may have server storage constraints that require you to control the number of backup versions allowed for logical volumes. The server handles logical volume backups the same as regular incremental or selective backups. Logical volume backups differ from selective, incremental, or archive operations in that each file space that is backed up is treated as a single large file.
Backups of logical volumes are intended to help speed the restoration of a computer. One way to use the capability is to have users periodically (for example, once a month) perform a logical volume backup, and schedule daily full incremental backups. If a user restores a logical volume, the program first restores the logical volume backup and then any files that were changed since the backup (incremental or other file backup processes). The user can also specify that the restore process reconcile any discrepancies that can result when files are deleted.
For example, a user backs up a logical volume, and the following week deletes one or more files from the volume. At the next incremental backup, the server records in its database that the files were deleted from the client. When the user restores the logical volume, the program can recognize that files have been deleted since the backup was created. The program can delete the files as part of the restore process. To ensure that users can use the capability to reconcile later incremental backups with a restored logical volume, you need to ensure that you coordinate policy for incremental backups with policy for backups for logical volumes.
For example, you decide to ensure that clients can choose to restore files and logical volumes from any time in the previous 60 days. You can create two management classes, one for files and one for logical volumes. Table 1 shows the relevant parameters. In the backup copy group of both management classes, set the Retain Extra Versions parameter to 60 days.
In the management class for files, set the parameters so that the server keeps versions based on age rather than how many versions exist. More than one backup version of a file may be stored per day if clients perform selective backups or if clients perform incremental backups more than once a day. The Versions Data Exists parameter and the Versions Data Deleted parameter control how many of these versions are kept by the server. To ensure that any number of backup versions are kept for the required 60 days, set both the Versions Data Exists parameter and the Versions Data Deleted parameter to NOLIMIT for the management class for files. This means that the server retains backup versions based on how old the versions are, instead of how many backup versions of the same file exist.
For logical volume backups, the server ignores the frequency attribute in the backup copy group.
| Parameter (backup copy group in the management class) | Management Class for Files | Management Class for Logical Volumes |
|---|---|---|
| Versions Data Exists | NOLIMIT | 3 versions |
| Versions Data Deleted | NOLIMIT | 1 |
| Retain Extra Versions | 60 days | 60 days |
| Retain Only Version | 120 days | 120 days |