Backup Exec is supposed to clear (prune) expired data on a regular basis but the process can mess up more often than not. The end result is you can run out of space on your media even though your jobs are set to “overwrite” older media.
The biggest cause of this kind of problem is inconsistent results with full backups. BackupExec will NOT delete old data sets, even if they are expired, if more recent full backups have not been successful nor will it let you overwrite those media sets.
To force the clean-up of old, expired data you need to do the following (all of this is predicated on BackupExec 2012, older versions may operate differently).
Go to your storage:
Click in to it then into the Backup Sets …
Scroll down to the bottom then highlight the items you want to delete …
Right-click the select Delete … then start answering questions …
Click Yes to all
Depending on what is in the backup set you want to delete you may get prompted as follows:
I want the data deleted so click Delete this set and all dependent backup sets …
This can take some time. The green progress bar will appear at some point and slowly update, be patient.
The process will repeat as BackupExec rolls through the backup sets you have selected, possibly prompting again for your input on deletion. The process can be quite lengthy as data is being deleted from storage media (like the QNAP) as well as catalogues are being pruned of references to the datasets. Removing a large amount of old data can easily take an hour or two so be prepared.
Once the process completes you will see that space has been freed on your storage media.
I was at 4GB free on the QNAP before the clean-up. More should clear up after the next full backup.