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I'm using Bacula but this would pertain to any backup solution.

I'm using LTO5 tapes (1.5TB/3TB), but my data is nowhere near that capacity for the time being. So if I set the retention for my incrementals to 4 weeks, what happens to the tape if it's not full? Does Bacula go to the next tape?

sdot257
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VolumeRetention in Bacula defines how long Bacula will retain a full tape for.

Once Bacula opens a tape it will continue writing (appending) to it until it is full (unless you have told it to only put one backup on a tape, in which case the tape will be considered "full" when the backup finishes).

A full tape starts the VolumeRetention clock -- Bacula will not recycle and reuse that tape until the VolumeRetention period has has elapsed.

For example, if you fill a tape on Monday at 08:00, and have VolumeRetention set to 3 days the tape will become eligible for recycling on Thursday at 08:01 (3 days from when it was filled).

See the Bacula manual section on Automatic Volume Recycling for more details.

voretaq7
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  • Ah, so it only goes into effect when the tape is FULL? Ok, so if I start a backup today (Jan) with a retention period of 1 month, but it takes 2 months to fill up. Does that mean I can't use the tape until April? – sdot257 Jan 23 '12 at 18:20
  • @luckytaxi Yup -- You can append to it until it's full, and once it's full Bacula won't purge it until the retention clock runs out. In your example if you start using it `Jan. 1` and fill it on `March 1` it becomes eligible for recycling on `April 1`. – voretaq7 Jan 23 '12 at 18:32