With the DFS Backup System, you control many aspects of the backup process, including how often backups are performed, which filesets are backed up, and whether full or incremental backups are made. A dump or dump set is the result of performing a backup operation; it includes data from all of the filesets that were copied onto tape at the same time. A full dump includes data from every file in a fileset; an incremental dump includes only those files in the fileset that changed since a previous dump was made. The backup process is also referred to as dumping a fileset family or creating a dump set.
Once a fileset has been dumped, the DFS Backup System can be used to restore it. When restoring a fileset, the DFS Backup System first restores a full dump of the fileset. It then restores the changes to the fileset from any incremental dumps that were made since the full dump. Two types of restores are possible: a full restore, which re-creates the fileset as it was at its last dump, including changes from the last full dump and any incremental dumps that were made since the last full dump; and a date-specific restore, which re-creates the fileset as it was at the time of its last dump before an indicated date. The Backup System restores the last full dump and any incremental dumps of the fileset that were done before the specified date, so the fileset is current according to the last dump made before that date.
Sparse files contained in the backup fileset remain mostly sparse when dumped or restored. Any 64 KB chunk of a file that contains actual data expands to fill 64 KB on the disk. However, if a 64 KB chunk does not contain data it does not require physical space on the disk. This 64 KB granularity is imposed to ensure high-performance data access.
The Backup System can be used in conjunction with a variety of automated backup devices, including stackers and jukeboxes. Through a user-defined configuration file, you can specify parameters to configure the Backup System's Tape Coordinator to control automated backup equipment. The Tape Coordinator can then call executable routines, change tapes, select the proper tape, and handle errors.
The Backup System can be used to dump and restore data between different types of file systems. For example, data dumped from a DCE LFS fileset can be restored to a DCE LFS fileset or to any type of non-LFS fileset. Likewise, data dumped from a non-LFS fileset can be restored to a DCE LFS fileset or to a different type of non-LFS fileset. Note that incompatible information may be lost when a fileset is dumped and restored between file system types; for example, ACLs on objects in a DCE LFS fileset may be lost if the fileset is restored to a file system that does not support ACLs. (Refer to your vendor's documentation to verify the level of support for dump and restore operations between different types of file systems.)
The Backup Database records the schedule for backups, the locations of the Backup System's Tape Coordinators, the groups of filesets (fileset families) that can be dumped, and other administrative information. One Backup Database exists per cell; it is used to back up data from all administrative domains in the cell. A master copy of the Backup Database is maintained on one machine and replicated on other machines in the cell. Ubik creates and synchronizes the master and secondary copies of the database. (See DFS Configuration Issues for more information about Ubik.) In addition, the DFS Backup System provides facilities to back up the database by copying it to tape so that it can be restored if necessary. You can also remove specific configuration and dump information from the database if needed.
The Backup Database is maintained by the Backup Server, or bakserver process. The Backup Server must run on each machine that stores a copy of the Backup Database. Only the administrative users and members of the groups included in the admin.bak administrative list can issue bak commands, which are used to configure and administer the Backup System and to back up and restore data. Like the Backup Database, the admin.bak file is installed on one machine (usually the System Control machine) and copied to all machines that house copies of the Backup Database.
Some operating systems have their own backup commands. If your operating system has commands named bak, make certain that you use the complete pathname (dceshared/bin/bak) when issuing DFS bak commands. Note that bak commands can presently be used to affect the Backup Database in the local cell only.
More:
Fileset Families and Fileset Family Entries
Dump Hierarchies and Dump Levels
Command and Monitoring Windows
Privileges Required to Use the Backup System