In a tape rotation system, multiple tapes are organized into a tape backup pool, or tape backup library to provide you with data recovery capabilities, whilst allowing for selected backup tapes to be stored off-site for added security.

Different tapes are used for different days' backups according to a predefined system. Three such tape rotation systems are described in the links to the right.

Different types of backups are available in backup software. Each will backup different amounts of data, and different types of files as summarized below:

A Full backup will copy all files and system data to the backup media. It allows for the complete restore of all data from one single tape.

Differential, Incremental and Daily are partial backups are designed to reduce amount of data backed-up to the media, resulting in faster backups. To restore data using one of these backups, the last Full backup tape will also be required, along with any other partial backups since the last Full backup.

For example, if Full backups are performed on Mondays, and Incremental backups on the other days, to restore last Thursday's data, 4 tapes would be required (Monday full + Tuesday incremental + Wednesday incremental + Thursday incremental).

The problem with partial backups is the requirement for multiple tapes when restoring data. If any of these tapes is faulty, then the restore cannot be guaranteed to proceed correctly.

Clearly, if all your data can fit onto a single tape, performing full backups all the time is the safest strategy.

*Information supplied under the Tracking | Tape Rotation section of DSC's website contains material from Backup Strategy Guide written by Linus Chang for the Windows Server Backup Software at www.backupassist.com/BackupAssist/bsg1.php and www.backupassist.com/BackupAssist/index.php