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Backup Intervals and Backup Withholding Periods
If each backup generation is kept forever, soon enough the backup disk will be full.
For example, a 2.5% change between backup generations, means 100% backup storage after 40 backup generation. If the backup frequency is twice a day, it means that each 20 days period, we will have to add 100% to the backup disk.
RRB has a mechanism to discard and manage the expiration of backup generations, retaining the selected ones.
It can simply retain the last X backup generations, making it possible to schedule backup sessions forever, without having to worry about managing the backup space.
Based on backup generation date, RRB can also execute differential expiration for older backup generations.
This mechanism allows longer backup withholding period, with the same backup space, and it is an adaptation of the traditional Grandfather Father Son (GFS) rotation, used in tape backup to disk while consuming a backup space that is 20-100 times smaller.
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