I have two tape silos attached to one backup master. I prefer that each silo be used by the Business Unit associated with that silo. But in case one silo goes down I allow the backups to run on the other silo. (Better to have the backups float to the other silo than not run at all).
So I have defined two storage groups - each has both silos defined (in opposite order of course). The Storage Unit Selection is set to "Prioritized". So I would expect Business Unit A's backup to normally run on silo A and Business Unit B's backups to normally run on Silo B.
But somewhat often I see 'A' jobs using the 'B' silo or 'B' jobs using the 'A' silo. My only guess is that Netbackup tries to Multiplex to an existing drive if it can - even if that drive is on the lower priority Storage Unit.
Does anyone know if this is what Netbackup is doing?