Prune Simulator Question

[Undergrid]

I've been using the prune simulator to figure out a decent backup schedule and I've come across something I don't understand.

The image below shows a daily backup with the following: keep_daily 7, Keep_weekly 4, keep_monthly 4, keep yearly 2.

The monthly backup appears to be kept for the last day of each month, which is logical. But the backup for the 31st march has already been deleted, the closest one remaining being for the 3rd of April. What happens when PBS gets to the stage where it should be keeping a backup for March?

 

[Matthias.]

There is no monthly backup in march because march is already covered by the weekly backup, just as there is no green in the first week which are covered by daily.
When choosing a monthly backup for march, there are still four backups, the green ones. It can take one of these.

I hope this helps, if not, please feel free to ask again!