What Are Browse and Retention Policies?

The Backup server maintains one file index for each client machine (regardless of the number of client resources configured for it) and one media database that tracks data from all clients. Each time a backup is completed, Backup creates entries for the backed-up files in the client file indexes. The media database stores one entry for each save set and storage volume during each backup operation.

Each client file index is a browsable structure of data from a single client machine. Users can specify anything from a single file to a complete filesystem and direct Backup to reconstruct the data during a recover session to look exactly as it did at a specific time. The information that the client index contains and coordinates enables Backup to automatically handle situations such as assembling data from backups based on levels, and to accommodate all file or directory renamings or deletions. Backup uses browse policies to manage the life cycle of data and to automatically control the size of the client file index.

The Failed Cross Reference Format determines how long files are maintained in the client's file index on the Backup server. During the period of the browse policy, users can browse backed-up data in the Backup recover program (nwrecover) and select individual files or entire filesystems for recovery. After the browse policy for a file is exceeded, Backup automatically deletes the entry for that file. Backup deletes these entries to manage the size of the client index, which can grow rapidly: one entry for each file backed up during each scheduled backup of the client.

The media database is the structure that tracks the location of save sets on storage volumes. Backup uses a Failed Cross Reference Format to manage the longevity of Backup managed data. Data is recoverable as long as entries exist in the media database; there is nothing to be gained by rushing to delete media database entries. For all these reasons, the media database retention policy does not trigger the automatic removal of media database entries. Instead, the retention policy determines how long an entry for a save set remains protected from being accidentally written over.

The retention policy determines how long save sets are maintained in the Backup server's media database. For at least the period of the retention policy, you can recover a client's backed-up save sets from media. No save set is considered recyclable until, at a minimum, it has exceeded its retention policy. No storage volume can be relabeled and written over until, at a minimum, all save sets on the storage volume have exceeded their retention policies. Theoretically, entries for a save set or a storage volume can remain in the media database forever, long after the retention policy has been exceeded. Entries are removed from the media database only if a storage volume is relabeled or if you manually delete the entries.