DFS provides two methods of managing backups: the DFS Backup System and backup filesets. With the DFS Backup System, you can copy data from filesets to tape and restore the data from tape in the event that the data is lost. Information about backups and tapes is maintained in the Backup Database. The database itself can be copied to tape and restored in the event of its corruption. Backups of both DCE LFS filesets and non-LFS filesets are supported.
You can perform both full and incremental backups, or dumps. A full backup copies all of the data in a fileset to tape; an incremental backup copies only those files that have changed since the last full backup to tape. A backup schedule, or dump hierarchy, records the specified filesets to be included in a backup.
You can restore data from tape in the same manner. A full restore re-creates the data as it was at its last backup, including any changes from the last full backup and any subsequent incremental backups; a date-specific restore re-creates the data as it was at a specific point in time, including data from any incremental backups done before the specified date. You can restore individual filesets or an entire aggregate.
The DFS Backup System supports automated backup devices, such as jukeboxes and stackers. By specifying parameters in a configuration file and writing the appropriate executable routines, you can enable the DFS Backup System to change tapes, select tapes, and handle errors.
Note: Sparse files, when copied through the DFS Backup System, do not expand to their full size. However, the sparse file copy has a minimum granularity of 64 KB, any chunk that contains no actual data requires no storage space on the tape.
Backup filesets capture the state of source data at the time the backup is made; they do not involve the Backup System. You can create a backup version of a user's DCE LFS fileset and mount it as a subdirectory of the user's home directory, naming it something appropriate such as .OldFiles or .BackUp. The user can then, without assistance, restore to a read/write fileset any files deleted or changed since the backup fileset was made. Users cannot change the data in their backup filesets, but they can copy the data to a regular directory in a working, read/write fileset and use it there.