Backup Retention

Is there a good place that explains the Backup Retention options?

The basic options are to keep backups forever, keep only a certain number of backups, or keep backups only under a certain age. Do you have questions about those options? Or are you asking about the more advanced retention policy option?

Ideally, what I would like, is for files to be “updated”. So for example, I have a file like a.doc. If I make a change to it, next time the backup runs, it “updates” that file - and there only remains one backup of that file.

Ok, it is important to note is that to duplicati a backup “version” is the entire backup snapshot. You can decide how many backup snapshots should be retained but it doesn’t work at the individual file level.

How does smart backup retention work? I want to make sure that backups do not fill up the entire FS.

Keep in mind that Duplicati only stores changes every time it does a backup, so you probably can have many, many versions without it necessarily taking a huge amount of back end storage. Obviously this will vary depending on how much data changes between backups on your system, the type of data, etc.

One of my backup sets has 227 versions that span more than 3 years. Source side is 28GB and backend size is 88GB.

The “smart” retention is basically a custom retention policy of 1W:1D,4W:1W,12M:1M. After a backup is completed, the retention policy is evaluated to decide what backup versions to delete. This particular policy basically says:

  • In the most recent 1 week, keep only 1 backup version per day.
  • Then, In the most recent 4 weeks, keep only 1 backup per week.
  • Then, In the most recent 12 months, keep only 1 backup per month.

This policy would delete any backup version over 12 months. Personally I don’t use it and instead use my own retention policy of: 7D:0s,3M:1D,2Y:1W,99Y:1M

What is the difference between 7D:0s and 7D:U ?
Are there more options?

There is no difference. From what I recall the “U” option was not available when the retention policy feature was first implemented, so using “0s” was how you did it if you wanted to keep all backups.

In addition to “U”? That’s the only special case letter I’m aware of. All the others are for units of time: D = day, Y = year, etc.

1 Like

Thank you for your explanation!