I took so long to write this that David G. beat me to the punch. My [lengthy] explanation below takes into consideration the implications of the Full/Block Backup sets I described in a prior post.
Backup Fan - Yes you are correct. It will purge based on the most aggressive purge setting, be it # of versions or days.
Keep in mind that the latest version of each file is always saved unless you deliberately uncheck that setting. There are situations where we do his but that is beyond the scope of this discussion.
If you back up a file such as a picture or pdf that never gets modified, it will remain in backup storage forever, regardless of any retention settings.
The settings only apply to files that get modified, creating multiple versions.
To continue for those hell bent on using # of versions, I will try to explain how it works using a different example.
- Retention set to Keep 2 versions
- Retention set to keep 30 days
- Fulls set to run weekly
- Day 1 - Full backup = V1
- Day 2 - Block incremental = V2
- Day 3 - Block Incremental = V3
You would think that V1 could be deleted, but it cannot since you still need V2 (in order to still have 2 versions) and V2 depends on the Full (V1).
- Now lets say that the file is not touched again until the Weekly Full Backup runs creating V4.
You still cannot delete any of the V1-V3 versions since they are considered a "set" and you cannot delete V3 for the same reason as above.
- The next day you run a block level backup (V5)
NOW V1 - V3 will be purged, since we now have two versions (V4 & V5).
Lets say that you do not modify this file again.
- The following week a new Full (V6) will get created as a full is taken for any files that have had modifications since the last full.
When V5 reaches 30 days old, can V4 and V5 be deleted? No, because V5 represents Version #2 and Since V5 is associated with V4, it cannot be deleted either.
Now if you did only fulls (by turning off block level backups), you would always have just the two most recent full backups of the file, but that will chew up more storage than an incremental does, particularly if you have files in the 100's of MB's.
If you are backing up files/versions for paying clients, I strongly recommend a 30 day retention - at a minimum - and do not use # of versions. We use 90 days as our standard, with some clients paying extra for 15 month's retention to protect versions of files that are only touched once per year or so (accounting, Law Offices, etc.)
This way it does not matter how many times each month the file gets updated, you can always go back to a version from 30 or 90 days ago. For some files, it might be two versions for others there may be 30 or 90 versions but in all honesty, at the hideiously low cost per TB of Cloud storage available these days, storage costs should be the least of your concerns.
Not being able to recover a file from a month ago because you only have the last two days due to your " # of version" settings will be far more painful.