I upgraded my workstation from FC1 to FC4 a couple of weeks ago. While moving stuff around, I bumped my external tape drive and it fell about a foot. Thinking nothing of it, I continued working.
I started to notice that my backups weren’t working. Thinking I might have a bad tape, I labeled a new tape, but got “this tape is write-protected”.
After working on it, and even taking apart the tape drive to see if I dislodged a connection, I was about to give up.
Then I Googled for the error message I got, and someone mentioned it might have to do with file permissions on /dev/nst0.
Argh. /dev/nst0 was set for 640 by way of udevd. Editing the st and nst lines in /etc/udev.d/rules.d/50-udev.rules fixed it. I had forgotten that FC4 uses dynamic device entries.