Maintaining Backup Indices in PresSTORE 4
Posted by Sven Koester on 14 April 2009 12:32

When creating backups, PresSTORE handles in background so called backup index databases automatically. In these databases PresSTORE keeps  the information which file is stored on which tape.

These index databases may consume a lot of disk space: as a rule of thumb, one kB is required for one file,one million files in the backup require 1 GB disk space. In case this requires too much space on the file system where PresSTORE is installed, PresSTORE can be moved to another location. This is described in the following article:

For each client in the backup, including the localhost client, index files are maintained separately.  For each full backup, a new set of index files is created, each incremental backup extends the existing index. After a while, multiple backup cycles and thus multiple sets of index files exist.

The content of all existing index databases, excluding files from recycled media, is visible in the index browser of the PresSTORE GUI. By default, only the newest cycle is presented; elder cycles can be reached using the index browse options in the menu.

When the last tape that holds (parts of) a backup cycle is recycled and thus deleted, the index cycle is also deleted and is no longer reachable in the index browser.
The only other way to delete a backup index is to remove the client in PresSTORE. In case a client is removed, the backup index for that client is removed, too.
Please note that when the index does not exist anymore, it is no longer possible to restore the files.

This behavior has been designed to keep backup and restore operations fast. On the other hand, PresSTORE relies on a new full backup taken in regular intervals. In case there are only incremental backups taken but never a full backup, the backup indices will grow and never get deleted.
(However this is not only related to the backup indices, that behavior also implies that the backup is spread over more and more tapes, so it may affect many tapes to restore a single directory, and there is no mechanism that takes care of worn out tapes).

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