Thanks to all who replied.
Original problem:
astro# mt -f /dev/rst8 rewind
/dev/rst8: Device busy
1) I've been using this drive in its current configuration
for a couple years.
2) There are no processes using /dev/rst8 that I can see.
3) Power cycling the drive has no affect.
Solution:
It wasn't necessary to reboot the machine. When I
said I couldn't find any processes using rst8, I was
grep'ing on the wrong string. The answer was to kill
/etc/rmt.
Again, thanks.
EJO