An Excellent Example About Veeam’s Incremental Backup Retention

By admin, August 22, 2011 13:50

A Good Example About Veeam’s Retention

Re: Job Set for 14 Mount Points – 46 exist
Posted: Thu Jan 20, 2011 4:57 amby tsightler

Logically your requirement to keep 14 restore points can’t be met until there are at least 14 more restore points from the last VBK.

In other words, you have a full backup, then 46 incrementals, then a full backup. If Veeam deletes the first full backup, and 33 incrementals, you’ll be left with 13 incrementals and a full backup, except those 13 incrementals will be worthless since the full backup on which they were based would be deleted. Setting the number of retention points for incremental backups sets the minimum number that will be retained. The maximum number might vary based on the interval that you run full backups (either active or synthetic).

This has been explained in another thread, but here it is again for simplicity. Let’s say you run backups every day, and you want to keep 14 restore points, and you run a full every week. After one week you get this:

Week 1: F…I…I…I…I…I…I

So that’s one full, and 6 incrementals, for a total of 7 restore points, now the second week:

Week 1: F…I…I…I…I…I…I
Week 2: F…I…I…I…I…I…I

So that’s two fulls and 12 incrementals for a total of 14 restore points, now it’s day 15, and you run another full and end up with this:

Week 1: F…I…I…I…I…I…I
Week 2: F…I…I…I…I…I…I
Week 3: F

You’ve told veeam to keep 14 restore points, but it can’t delete the full backup from week one, because that would invalidate all of the incremental backups from week 1 and leave you with the following:

Week 2: F…I…I…I…I…I…I
Week 3: F

That’s only 8 restore points, and you’ve told Veeam to keep 14. Veeam will not delete the first weeks backups until the last backup of Week 3 because at that point you’d have 21 backups:

Week 1: F…I…I…I…I…I…I
Week 2: F…I…I…I…I…I…I
Week 3: F…I…I…I…I…I…I

Thus if Veeam deletes Week 1 I get:

Week 2: F…I…I…I…I…I…I
Week 3: F…I…I…I…I…I…I

14 backups, which meets the requirement.

If you want Veeam to keep the exact number of restore points you can use reverse incrementals since in that case the oldest backup can always be deleted, otherwise, it’s no different than tape backup retention has been forever, the ratio of full to incremental backups will determine the number of backups that have to be kept to meet a minimum retention period.

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