What is backup rotation?
Backup rotation is a schedule for reusing backup media or storage. It decides which backups are overwritten, which are kept and for how long, so that a limited set of media provides restore points going back days, weeks and months. The term comes from tape, where physical cartridges cycle between the drive, a shelf and an offsite vault.
What rotation schemes are used?
Schemes differ in how many media sets they need and how far back they reach.
| Scheme | How it works | Result |
|---|---|---|
| First in, first out | A fixed number of sets, oldest overwritten each run | Simple, history only as deep as the set count |
| Grandfather-father-son | Daily, weekly and monthly sets with different reuse cycles | Dense recent history, sparse older history |
| Tower of Hanoi | Sets reused at doubling intervals | Long reach with few sets, harder to follow |
| Weekly full with daily increments | One full set per week, increments in between | Common with tape libraries |
Why does rotation include moving media offsite?
With tape, rotation is physical as well as logical. Recent sets stay on site for quick restores, older sets go to a vault, and expired sets come back for reuse. The movement is what provides the offsite copy and the separation from the network. It also introduces the risks of the method: missed collections, mislabelled cartridges and media that has been through more cycles than it should.
What does rotation mean on disk and object storage?
On disk and object storage there is no media to swap. The backup software applies a retention policy and deletes restore points when they expire. The scheme, usually GFS, survives as a set of retention rules. What used to be achieved by ejecting a tape is achieved by a second copy at another location and by immutability, which stops restore points being removed before their time. Offsite backup without tape rotation describes the transition.
How is a rotation scheme chosen?
The scheme follows from recovery needs. How far back must restores reach, and how precisely? How much data can be lost between restore points? How much media or capacity is available? A scheme that keeps a month of daily points and a year of monthly ones serves most operational restores. Longer or denser history costs more media or storage, and should be justified by a specific requirement. Retention policy design covers the reasoning.
Frequently asked questions
Is backup rotation the same as retention?
They are closely related. Rotation is the schedule for reusing media. Retention is how long each restore point is kept. On disk and object storage, retention has largely replaced the idea of rotation.
How many tapes does a GFS rotation need?
It depends on the tiers. A common small scheme uses four daily, four weekly and twelve monthly sets, about twenty in all.
Does rotation protect against ransomware?
Only the sets that are offline or immutable at the time of an attack are safe. Sets still reachable by the backup server can be overwritten.