A Backup rotation scheme is a method for effectively backing up data where multiple media (such as tapes) are used in the backup process. The scheme determines how and when each piece of removable storage is used for a backup job and how long it is retained once it has backup data stored on it. Different techniques have evolved over time to balance data retention and restoration needs with the cost of extra data storage media. Such a scheme can be quite complicated if it takes incremental backups, multiple retention periods, and off-site storage into consideration. In information technology, backup refers to making copies of data so that these additional copies may be used to restore the original after a data loss event. ... Magnetic tape has been used for data storage for over 50 years. ...

Schemes

Incremental backup

• Used to keep the longest possible tail of daily backups
• Archived backups not as important (ie no need to go back 1 year)
• Useful when data before the rotation period is irrelevant

Basically the incremental backup is just backing up onto the oldest media in the set. So with a daily backup onto a set of 14 media, you would have 14 days worth of individual daily backups, when all the tapes are used, the oldest one is inserted.

This is the simple method that first comes to mind to most new computer users wanting to do backups. It was commonly used when people backed up regularly to floppy disks.

Grandfather, Father, Son

• Keeps a longer archival process
• Have more copies available of recent backups, and progressively less as you need to go back over time.

This is one of the most popular method as it achieves multiple aims in having multiple recent backups as well as the ability to refer to past revisions as well as archived data.

Refer specifically to Grandfather-Father-Son Backup. Grandfather-Father-Son Backup refers to the most common rotation scheme for rotating backup media. ...

Towers of Hanoi

The Towers of Hanoi (TOH) backup rotation method is based on the ancient mathematical progression puzzle called Tower of Hanoi. The goal of this backup scheme is to put changed files on more than one storage medium while at the same time reducing overall storage volume. This method assumes that each changed file is backed up twice and recorded to two different storage media. A model set of the Towers of Hanoi An animated solution of the Tower of Hanoi puzzle for T(4,3). ...

According to this method each consecutive incremental backup has a level from 0 to 9, where each backup in the hierarchy can back up only what has changed since the last lower level backup.

The backups are distributed in time so that each changed file is backed up twice.

Weekly Towers of Hanoi schedule

The level 0 backup that takes place on Sunday is a full backup of all data. The level 3 backup on Monday is an incremental backup of everything that has changed since Sunday. The Tuesday level 2 backup records everything that has changed since Sunday (not since Monday, as Monday backup is higher in the hierarchy), thus it includes the changes recorded on Monday and all other changes that have taken place since Sunday. The Wednesday backup records only what has changed since Tuesday, i.e. since the last lower level backup. The Thursday backup records all changes since Tuesday including changes recorded on Wednesday. The Friday backup includes changes done since Thursday; and finally the Saturday backup records all changes since Thursday including those recorded on Friday.

It should be noted however, that the changes that take place on Tuesday are recorded only once (during Tuesday backup), while all other changes are recorded twice. To get around this problem, a modified TOH progression, dropping down to a level 1 backup each week, may be used.

Monthly Towers of Hanoi schedule

The monthly Towers of Hanoi schedule makes sure that all changes that have taken place since the monthly full backup (0 level backup) are recorded once a week on Sunday (level 1 backup). The TOH method is believed to protect against media failure better than any other backup rotation method.

Incremented media method

This method has many variations and names. A set of numbered media is used until the end of the cycle. Then the cycle is repeated using media numbered the same as the previous cycle, but incremented by one. The lowest numbered tape from the previous cycle is retired and kept permanently. Thus, one has access to every backup for one cycle, and one backup per cycle before that. This method has the advantage of ensuring even media wear, but requires a schedule to be precalculated. The system is generally too complex to mentally calculate the next media to be used.

See also

• Backup
• Incremental backup
• Off-site Data Protection