Friday, March 20, 2009

Backup Client - Incremental (inc) versus Selective (sel)

Both Incremental or inc and Selective or sel backups are available from the Tivoli Storage Manage backup client. These two backup methods are considerabley different.

Incremental does mainly what it says - it backs up all files that have been added or changed on the file system since the last backup. This is affected by the exclude/include information in the configuration file. In addition, specific files can be backed up by selection from the command in the command line client. In addition the frequency and mode on the managmement class's Copy Group can affect if the file is included. The frequency affects how often the file can be backed up. The mode can cause it to be backed up whether it has changed or not.

Selective is meant to be used for exactly what the name indicates. Selecting individual files for backup. It is to be used mainly if the backup of a file or set of files is know to be damaged. By doing a selective backup, the file can be put into the TSM server again. Care must be taken with the use of Selective backups as more files than intended can be backed up and will affect the number of inactive files being retained. If the policy is for 5 inactive copies to be retained, and a selective backup is made before the file changes then 2 of the copies are identical.

So, unless there is a specific need, use the incremental backup rather than the selective.

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