Friday, September 03, 2010

Solution: DPM 2010 tape backup rotation (re: DPM keeps on $#*%!& appending)

Problem: You're using Data Protection Manager (DPM) and your tape backup keeps on failing when you try to overwrite an expired backup. You get something like this:

The back up to tape job failed for the following reason: (ID: 3311)

Failed to perform the operation since the tape free tape is not available in ...

Using new tapes, tapes marked as free and the powershell free tape script work though.

Solution: Use 1 more tape than you think you need in your rotation.

I've spent the last week or so struggling with getting this backup working the way I think it should (for some reason I managed to get this setup on DPM 2008 without any problems). Including a few days manually running the free tape powershell script. I just thought that was asking for trouble since we use a single drive not a library. Somehow I know I'm going to wipe a tape I didn't mean to wipe.

During my googling I found several people that were in the same boat as me. RE: Wanting to use 8 tapes containing 4 weeks of backups:

  • 4 tapes: full backup on days Mon, Tues, Wed, Thu
  • 4 tapes: full backup every Friday for 4 weeks (Fri_1, Fri_2, Fri_3, Fri_4)

That allow me to go back four days or up to a month. It's not perfect but it's a reasonable amount of tapes to manage. DPM kept on giving me errors about a tape not available because it didn't delete the expired content on the tape first.

DPM will only re-use the tape if everything is expired on the tape. Looking at the expiry dates on the tape it seemed like it should be expired but it never was. DPM kept on appending to the tape. So I now have the following setup and it seems to be working so far. I just added 1 tape to each rotation to give me a 1 day buffer. That way DPM will always see a tape about a day old:

  • 5 tapes: full backup on days Mon, Tues, Wed, Thu (A, B, C, D, E)
  • 5 tapes: full backup every Friday for 4 weeks (Fri_1, Fri_2, Fri_3, Fri_4, Fri_5)

The downside is for the weekdays, I can no longer identify the tapes by day, I need to use a calender. Tough enough being awake on monday but to remember what tape I used for the past's not going to happen. Hopefully, this will help someone, I like DPM overall just don't agree with the tape backup rotation strategy.

Note: after figuring this out for myself I finally found a small reference on Microsoft's support website:
Tape Rotation Does Not Work As Expected When DPM is Utilizing a Tape Only Solution

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