I have what I think is a pretty standard setup. We have a tape library with 2 drives, we backup 15 or so servers using a selection list per server and a single policy which does the scheduling etc.
We have recently upgraded our tape libraries from LTO4 to LTO5, so we have finished filling out our new tape rotation and are running through the tapes for the second time.
All the backup jobs are scheduled to run at the same time (as you would expect when they're all running off the same policy) and I use priority settings to make sure the critical servers get backed up first. The policy is set to append to media if possible and overwrite if necessary (this is according to best practice for multiple tape setups, right?). There is a nominal overwrite protection of 6 hours on the tapes.
Here is the situation: I end up with 2 jobs queued, waiting for a new tape. Both tapes in the daily rotation are full. Most backups miss their schedule some small amount of data gets written to tape. What seems to happen is that the tapes have had some data written to them and they are both (just for example) 75% full from the first run through of the tapes in the rotation. On the second run, the policy decides to append to the tape, runs through the last 25% and then starts looking for a new tape. Since both tapes available are now full, it will sit and queue forever.
Now, I know there are a couple of ways that I can manually work around this problem but I've gone to considerable trouble to setup our backup jobs according to Symantec best practice and I'm wondering if I'm not understanding something or if I'm in some kind of very unusual situation where best practice just doesn't produce reliable backups.
tl;dr summary; best practice backups starting with 3/4 full tapes and set to append/overwrite will fill up the tape and queue. What's up with that?