# fuser /dev/rmt/0cbn
# ps -ef | grep 10249
root 10249 11204 0 16:09:00 ? 128:22 /usr/sbin/nsrmmd -n 5
On some systems you may wish to use fuser -u <path> or fuser -cu <path>. On some systems it won't work (like HPUX 11.31).
Anyway, once you know the process id (eventually, lsof can be used too), you can use kill command against process. Where fuser works fine, fuser -ku <path> will kill it too.