Excerpt from the "Help Topics":
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The image catalog has information about all client backups and is accessed when a user lists or restores files. NetBackup allows you to 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, Compress catalog interval. 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, Compress Catalog Interval is set to 0 and image compression is not enabled.
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 impact 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 can accomplish two objectives:
•To reduce greatly the disk space that is consumed.
•To reduce the amount of 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, you may need to increase the time-out value that is associated with list requests. Change the time-out value by changing the List Files Timeout General property setting on the client.
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