How to correct "device busy" without reboot?

[Peter Steele]

Since we have upgraded to SunOS 4.1, we've been having problems with our
9-track tape drive. Occasionally, when we're doing dumps and have to mount
another tape, dump keeps complaining that the tape drive isn't ready and
we have to abort the dump. This then puts the tape drive in a state where
we get the error "device /dev/rmt12 is busy". The only way we've found to
clear this condition is to reboot the Sun. This condition is caused both
by dumps and by rdumps from another machine. We've tried rebuilding the
device drivers for xt0 (at the suggestion of Sun) but this did not fix the
problem. Anyone out there know what's going on? Thanks.