If you get this message from your QNAP:
The file system is not clean. It is suggested that you run "check disk"
and after you start a disk check and you end up with message like this:
[Mirror Disk Volume: Drive 1 2 3 4] Examination failed (Cannot unmount disk).
You need to get into SSH and execute following:
/etc/init.d/services.sh stop /etc/init.d/opentftp.sh stop /etc/init.d/Qthttpd.sh stop umount /dev/md0 e2fsck -f -v -C 0 /dev/md0 mount /dev/md0 reboot
After all of above, your QNAP NAS will reboot and everything will get back to normal.