About image catalog compression
The image catalog contains information about all client backups. It is accessed any time a user lists or restores files. NetBackup lets you compress all portions of the catalog or only older portions of the catalog. No method selectively compresses image catalog files other than by age.
Control image catalog compression by setting the Global Attributes property, . Use this property to specify how old the backup information must be before it is compressed. Specify the number of days to defer compression information, thus users who restore files from recent backups are unaffected. By default, is set to 0 and image compression is not enabled.
See Global Attributes properties.
Note:
Veritas discourages manually compressing or decompressing the catalog backups with the bpimage -[de]compress command or any other method. Manually compressing or decompressing a catalog backup while any backup (regular or catalog) is running results in inconsistent image catalog entries. When users list and restore files, the results can be incorrect.
It does not make a difference to NetBackup if the backup session was successful. The operation occurs while NetBackup expires backups and before it runs the session_notify script and the backup of the NetBackup catalogs.
The time to perform compression depends on the server speed and the number and size of the files being compressed. 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 the compression. To minimize the effect of the initial sessions, consider compressing the files in stages. For example, begin by compressing the records for the backups older than 120 days. Continue to reduce the number of days over a period of time until you reach a comfortable setting.
Compressing the image catalog accomplishes the following objectives:
Reduces greatly the disk space that is consumed.
Reduces the media that is required to back up the catalog.
The amount of space that is reclaimed varies with the types of backups you perform. Full backups result in a larger percentage of catalog compression than incremental backups. Normally, more data is duplicated in a catalog file for a full backup. Using catalog compression, a reduction of 80% is 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, increase the timeout value that is associated with list requests.
Change the timeout value by changing the General property setting on the client. Or, on UNIX clients, change the timeout value by changing the LIST_FILES_TIMEOUT option in the bp.conf file.
