Knowledgebase: Using tape drives
What is recycling and how does it work
Posted by Sven Koester on 23 April 2007 10:15
Q: How is the expiration date for volumes calculated?

A: The expiration date of a volume is set when the volume is involved by a backup plan. It is calculated based on the number of cycles chosen and the schedule of full backups defined in the plan. E.g. if a full backup is set up for Monday and Thursday and 1 cycle should be maintained, then a plan running on Monday will set the expiration date to Thursday. Several plans with different schedules can use the same pool, but the expiration date will never be set back, only forward, to reflect the longest period the data must be maintained. The current backup cycle of any plan will not be overwritten regardless of the expiration date setting.


Q: Which recycling policies are available?
A: There are two possible recycling policies:
  1. When volumes are needed. This policy keeps the data on the media as long as possible before recycling the volume. If further volumes are required, newly formatted empty volumes are preferred. Otherwise, only filled volumes (with status "full") or closed volumes (with status "closed") are considered for recycling.
  2. When the expiration date is reached. This is a greedy policy. It will attempt to recycle a volume as soon as the expiration date is reached. The status (full, closed, appendable) is disregarded. New empty volumes will be involved only when already written ones are not available. Note that when this policy is set, volumes are never flagged "recycleable" but are recycled immediately.

Q: When is the volume set to closed?

A: Written volumes are deemed "closed" when the pool is configured to use new volumes when starting a new full backup. The moment a plan employing such a pool is initiated, any volumes that have previously been written to, but are not yet full, will be closed. Closed volumes are recycled the same way as full volumes.


Q: Why are my volumes not automatically recycled?
A: Volumes are not recycled for one of the following reasons:
  1. Their expiration date has not yet been reached
  2. There is space left on the volume and it is not closed
  3. The volume is flagged suspect because of an error that happened on that tape
  4. The volume is flagged recycleable, but there are other empty tapes and the policy is set to "When volumes are needed".
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