Summary
DPX retains data in the catalog based on the retention period" set for jobs, and tapes are retained as long as there are unexpired jobs on the tape. Understanding how this is calculated can help an administrator optimize media rotation and management. "
Resolution
Any tape that has unexpired data on it will not be overwritten. If a tape is Appendable, backups may be written after the current data. However, a single backup that has not expired at the end of a tape will result in the tape not being reused.
When a backup job runs, a retention period is set based on the job's definition (base, incremental, or differential). Retention is measured in days, and can later be adjusted manually through the GUI's Catalog Job Functions. Expiration is calculated from the time the backup starts, so if a job runs at 5am on January 1 with a retention period of 5 days, it will expire at 5am on Jan 6. Expired jobs are removed from the catalog the next time a condense operation is run. In this example, if the condense runs before 5am on January 6, the job will not have expired yet, so it will remain in the catalog until the next condense after its expiration at 5am.
Therefore, if you have a tight media rotation schedule, set the retention period to one day less than the rotation period, and schedule a daily condense job. This will ensure that tapes become available before your backup jobs start.