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Tower of Hanoi backups

Tower of Hanoi backups

Rick Cook

Although most multimedia backups are done using a variation of the son-father-grandfather rotation scheme, there are other methods. The next most common is probably the "Towers of Hanoi" system, named for the ancient game it resembles.

Essentially the Towers of Hanoi involves backing up at multiple levels with each level being backed up half as often as the level immediately below. Thus if you make your first generation backups every other night, your second generation backups are created on the first night that isn't a first-generation night and repeated every fourth night, your third generation backups are created starting on the first night that isn't a first or second backup night and repeated every eighth night, and so on for as many layers of backup as you feel you need.

This is complicated but it offers several advantages. For one thing it offers a flexible rotation schedule because you can have as many layers of backup as you feel you need. It also means the site has fresher full backups than the usual generational scheme with incremental backups every night and a full backup once a week. Smaller sites that are more concerned with restoration and tape costs than long-term storage usually use it.

For a discussion of the Towers of Hanoi rotation and other topics related to data integrity, see:

Rick Cook has been writing about mass storage since the days when the term meant an 80K floppy disk. The computers he learned on used ferrite cores and magnetic drums. For the last twenty years he has been a freelance writer specializing in storage and other computer issues.

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