Amanda Faq-O-Matic :
How do dumpcycle, runspercycle and tapecycle control the behavior of Amanda backups?
The dumpcycle setting tells Amanda when to do a full backup, with the help of the runspercycle setting. For example, a dumpcycle of "7" in combination with a runspercycle of "5" completes at least one full backup by the seventh day, even in the case of having done only five runs. In the case where both values were set to "7" but fewer runs were completed over that period, Amanda might need further runs to actually complete its cycle.
Setting dumpcycle to zero gets Amanda to attempt a full backup on each run. (Amanda would only fall back to an incremental backup if there were insufficient tape space, or there were a tape error, etc.)
The tapecycle value tells Amanda when it can overwrite tapes. In other words, the tapecycle value is the way of telling Amanda how many tapes are in rotation. Putting a tape in sooner than its turn in the cycle will generate an error. Amanda will refuse to write the failed backup to tape until the correct tape (or a tape with an unused label) is inserted. In order for Amanda to run correctly, the tapecycle number should be at least one larger than the number of Amanda runs per cycle. A smaller number of tapes creates a risk of overwriting a tape before its equivalent has been backed up. It is possible to set the number lower and not get a complaint from the software. Obviously, the tapecycle value is not so critical if all backups are full backups, although it is nice to have at least a couple of successful backups in addition to the tape about to be clobbered.
Tapetype: Tandberg SDLT220