A backup & disaster recovery plan is a blend of protecting both data & hardware. Data & hardware protection falls into three basic categories: fault tolerance, mirroring or duplication and archived backups.
Fault tolerance
Though Fault tolerance is not a part of backup but it is very much like having a quick-fix or spare parts available at all times, and is often coupled with mirroring or duplication, as well. The goal of fault tolerance is either continuous operation or quick recovery. Fault tolerance for hardware can be as simple as having two Ethernet cards, so that if one dies, the other continues working - or as complex as building a clustered server with duplicates of everything. Fault tolerance can be applied to some degree to individual documents so that if they're trashed or deleted, they can be quickly recovered. Fault tolerance should be applied to group work and group communications systems to provide continuous operations in the event of hardware failure.
Duplication & mirroring
Both of these processes aim at the same goal: creating an exact replica of the primary source and maintaining that replica on its destination. Mirroring pertains to hardware. The process of attaching a second drive so that the data written to the first is automatically written to the second. Duplication (aka replicaiton) - the copying of files from a source computer to a protected destination computer - is an integral part of the backup process that pertains to all data types, whether the data is a document, a database, or an email system. Pointing your backup software at your computer's hard drive and telling it to back up everything (create a full backup) to a tape is a form of duplication because the contents of both the computer and the tape contain the same thing.
The goal of duplicating & mirroring is quick recovery during a disaster.
The mirrored duplicate of a primary data source or an entire groupwork server exists solely to be put into play when the primary fails. Restoring data from a full backup is the fastest restoration from a tape backup. Both data & hardware can be mirrored or duplicated. Whether the protection plan is to duplicate the data, mirror the hardware, or mirror the hardware and duplicate the data the goal is the same - quick recovery in case of failure or loss.
Archived backups
Archived backups take a "snapshot" of data and then place the snapshot in a safe destination. Every time you backup to tape, you copy the original source data onto that tape. Backing up a second time without erasing the tape (known as a normal backup) creates a second, dated copy of the original files. You now have a historical record - day one's files and day two's files. You can restore either day one's files or day two's files, depending upon your needs. This process is called creating an archived backup and is different than a full backup in that it has a dated history of files instead of an exact replica. Point-in-time restoration is the purpose of an archived backup. You don't back up hardware systems; only the data that lives on them.
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