Grandfather-Father-Son Rotation
What the Grandfather-Father-Son Scheme Is
Grandfather-father-son backup is a rotation scheme that keeps three tiers of copies: daily sets, called sons, weekly sets, called fathers, and monthly sets, called grandfathers. Each tier keeps a different amount of history, so the scheme gives both recent detail and long-term depth.
The idea comes from tape backups, where tapes were reused in cycles. It still applies to disk and cloud storage, because the question it answers is the same: which copies should be kept, and for how long?
The scheme sets the shape of your retention. The broader reasons for how long to keep data are covered in backup retention policy.
How the Three Tiers Rotate
Each tier has its own retention window, and older copies are replaced as newer ones arrive.
- Daily (son). One copy per day. Daily copies are kept for a short window, such as the past week, and each new one replaces the copy that falls outside the window.
- Weekly (father). One copy per week, taken from the same daily cycle. Weekly copies are kept for several weeks.
- Monthly (grandfather). One copy per month, kept for a year or more. Because there are few of them, they give long history at modest storage cost.
Many implementations use full backups for each tier, so each set can be restored on its own. The choice between full and incremental copies within the scheme is covered in full vs incremental vs differential backup.
A Corruption Found Six Weeks Later
A site's database begins to lose rows after a faulty import. The owner does not notice until six weeks later, when a customer reports missing orders. By then, the daily and weekly copies from the past month all contain the damage.
The monthly copy from before the import is still intact. Restoring it recovers the lost records, which could not have been recovered from the recent sets. Without the monthly tier, the owner would have had to rebuild the orders by hand.
Frequently asked questions
How Many Copies Does a GFS Scheme Keep?
The total depends on how many daily, weekly and monthly copies you retain. For example, keeping seven daily, four weekly and twelve monthly copies gives 23 restore points. Adjust the numbers to match your storage and how far back you need to go.
Does GFS Replace a Retention Policy?
No. A retention policy states how long copies must be kept, while GFS is one way to meet that policy. GFS shows how to arrange daily, weekly and monthly sets so that the policy is met with a manageable number of copies.