One of my tapes recently filled up and I went through the process of labeling a new tape and waited for my nightly backups to take place. For some reason, my backups didn't work, and when I type in "mes" to view my messages, I get this error:
16-Jan 08:43 bacula-sd JobId 1008: Error: block.c:1012 Read error on fd=6 at file:blk 0:0 on device "LTO-2" (/dev/nst0). ERR=Input/output error.
From what I've found using Google this appears to be a pretty common error that happens when you put a new tape in, and for the most part it doesn't really mean anything; but my backups didn't run.
So I just figured I'd try to unmount this tape, throw another one in there and label it, however I can't unmount it because I get this message:
3902 Device "LTO-2" (/dev/nst0) is busy in acquire.