Server Fault is a question and answer site for system and network administrators. It's 100% free, no registration required.

Sign up
Here's how it works:
  1. Anybody can ask a question
  2. Anybody can answer
  3. The best answers are voted up and rise to the top

I am trying to setup Symantec Backup Exec 12.5 to do a weekly full backup to an external USB drive. I would like to keep the last two weeks of full backups for the following reason: Example: If I happen to have a physical disk failure while my weekly full backup is running I could loose everything because I don't have a single complete backup. That is why I also want to keep the previous week's full backup.

I have read An explanation of the "Overwrite Protection Period" and the "Append Period" and I have not been able to figure out how to set the proper overwrite protection period for this type of backup. My understanding is that the OPP applies to the entire Media set and not just a particular backup job that is on the media. Every time a backup job is appended to a Media the OPP gets extended.

Lets say I setup a media set with a 13 day OPP and then setup a weekly full backup with append otherwise overwrite.

  • 1st week backup completes
  • 2nd week backup appends to media and completes
  • 3rd week backup fails because disk is full and the media set still has another 7 days left on the OPP.

Am I misunderstanding how OPP works on media sets? Is what I am trying to do even possible with a single media set?

Or do I have to do this with two different backup jobs and media sets? For example using a schedule like this:

  • 1st Sunday backup to Media1
  • 2nd Sunday backup to Media2
  • 3rd Sunday backup to Media1
  • ...
share|improve this question

You're understanding OPP correctly. The OPP period is calculated from the date of the last write operation to the media.

If the USB is large enough for 2 weeks of backups before it becomes full then simply use two USB drives: One drive for weeks 1 and 2 and another drive for weeks 3 and 4. Then set your OPP to 14 days.

If your first full backup starts on the 1st (week 1) and the last write to Media1 is on the 14th (week 2) then the OPP would extend to the 28th. You then begin week 3 with Media2 on the 15th going through the 28th. When the cycle begins again on the 29th Media1 is overwriteable again.

share|improve this answer
I am not asking about keeping 4 weeks worth of backups and I don't want to buy more USB drives. Can this be done with one backup job or do I have to create two backup jobs for this? – wtip Nov 2 '11 at 16:32
My answer is merely an example of how the OPP works. If you set the OPP to 13 days then the media is not overwriteable until 13 days past the last write to the media. Adjust the OPP accordingly, based on your needs. – joeqwerty Nov 2 '11 at 16:34
Let's take this one step further and say that I want to create daily differential backups and I want to keep them for a week. Am I going to have to create 7 different backup jobs and medias for every day of the week? – wtip Nov 2 '11 at 16:40
If you create backup jobs that target a particular media set and the OPP is 7 days then you can't overwrite that media set until 7 days after the last write to that media set. I see 1 backup job and media set for week 1 (full and differentials) and another job and media set for week 2. On week 3 media set 1 is overwriteable again if you're using a 7 day OPP, which is exactly what you stated in your question. I might recommend running a full backup and incrementals rather than a full and differentials. You'll use less space for incrementals than with differentials. – joeqwerty Nov 2 '11 at 16:53

You've understood the OPP correctly - any media will not be overwritten until all backup sets on that media are at least as old as the OPP.

I think there are a few things you might want to do.

The first is that you haven't mentioned anything about the size of the backup-to-disk files you're using. Each backup-to-disk file is considered a separate piece of media by Backup Exec. It's not the backup-to-disk device that gets the protection. If you use the default (IIRC) setting of 4GB for B2D files, your backup will presumably consume multiple B2D files (which is fine).

Secondly you haven't mentioned the APP period you're using at all. This effectively determines how long a single piece of media can be used for. You want to set this to a bit longer than the time it takes for a backup to run, say 24 hours or so. That way, when you come to do your second backup, it won't use the same media as the first backup.

Thirdly, you should probably set your Media Protection Option to overwrite scratch media before using new media. That way your B2D files which are out of their OPP will be reused, rather than filling up your disk with new files.

share|improve this answer

Your Answer


By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.