Compressing the Image Catalog

The image catalog has information about all client backups and is accessed when a user lists or restores files. NetBackup offers you the option of compressing all or older portions of this catalog. There is no method to selectively compress image-catalog files other than by age.

Control image-catalog compression by setting the the Global NetBackup attribute, Compress Catalog Interval. This attribute specifies how old the backup information must be before it is compressed, thereby letting you defer compression of newer information and not affect users who are listing or restoring files from recent backups. By default, Compress Catalog Interval is set to 0 and image compression is not enabled.

See Global Attributes Properties.

If you choose to compress the image catalog, NetBackup uses the compress command on the server to perform compression after each backup session, regardless of whether successful backups were performed. The operation occurs while the scheduler is expiring backups and before running the session_notify script and the backup of the NetBackup catalogs.

The time to perform compression depends on the speed of your server and the number and size of the files you are compressing. Files are compressed serially, and temporary working space is required in the same partition.

When numerous compressed image-catalog files must be processed, the backup session is extended until compression is complete. The additional backup time is especially noticeable the first time you perform compression. To minimize the impact of the initial sessions, consider compressing the files in stages. For example, you can start by compressing records for backups older than 120 days and then reduce this value over a period of time until you reach a comfortable setting.

Compressing the image catalog can greatly reduce the disk space used as well as the amount of media required to back up the catalog. The amount of space you reclaim varies with the types of backups you perform. Full backups result in a larger percentage of catalog compression than incremental backups because there is normally more duplication of data in a catalog file for a full backup. A reduction of 80% is sometimes possible.

This reduction in disk space and media requirements is achieved at the expense of performance when a user lists or restores files. Since the information is uncompressed at each reference, performance degradation is in direct proportion to the number and size of compressed files that are referenced. If the restore requires numerous catalog files to be uncompressed, you may have to increase the time-out value associated with list requests by changing the LIST_FILES_TIMEOUT option in the bp.conf file of the client.