I have a NetBackup 6.0MP7 installation running on Windows Server 2003. It functions as the only Master Server and Media Server. I swap a full set of tapes in and out every week, but leave a set of tapes with their Volume Pool set to "Scratch" in all the time. The weekly tape sets then get rotated back in after a period of time. Largely, this works fine. I seldom actually need the scratch tapes, but every once in a while, a backup will run over what I have dedicated to the task.
However, one week's set of tapes consistently gets declined in favor of the scratch pool. The backup policies are the same for every week, they all have "Policy Volume Pool" set to "NetBackup", and all of the tapes for every week (beside the scratch tapes) have had their pools assigned as "NetBackup", definitely including the week that always gets ignored.
That said, it doesn't ignore all of the NetBackup pool tapes for that week. It does usually write to two or three of them, but it writes to like 20 of the scratch tapes. (I haven't thought to look to see if it's always the same two or three tapes.) And this problem never seems to occur for any other week.
It doesn't load the tapes and then reject them; it never seems to try to use them at all. They are not flagged as frozen. They are all active and unassigned when I swap them in.
The tapes are in a Quantum PX510 tape library. The NetBackup server is attached to the library/robot via fibrechannel going through an HP-branded Brocade switch.
I'm not an expert on NetBackup at all. I don't really even know where to look. Any advice on logs to look at or logging to enable or really anything at all would be appreciated. I'll keep an eye on the question and update it if anyone needs any more info to help.