On my NAS QNAP TS 509 I do have a technical issue. I need to run e2fsck. This works fine for me on md0 (see below), but how can I unmount the busy devices md9 and sda4 in order to do the same. Whenever I try, I fail because the device is busy. [This part is solved, see below]

In order to further track down the issue, I'd need to sort out the physical disk to device relationship. How can I find out this, e.g. md0 is a stripped volume on 2 disk (but I need to find out on what physical disk).

Remark: As you can easily derive from my questions, I am not a Linux expert, but manage to get along.

/dev/ram0               124.0M     94.1M     29.8M  76% /
tmpfs                    32.0M     80.0k     31.9M   0% /tmp
/dev/sda4               310.0M    103.9M    206.1M  34% /mnt/ext
/dev/md9                509.5M     39.2M    470.2M   8% /mnt/HDA_ROOT
/dev/md0                  1.8T      1.4T    444.7G  76% /share/MD0_DATA
tmpfs                    32.0M         0     32.0M   0% /.eaccelerator.tmp

-- Added --

QNAP seems to be based on Busybox. I do not find something like init / telinit / runlevel. At busybox docs it says that I need to run the below. But in /var/service sv is not available. I want to go to single user mode to unmount the devices.

   # cd /var/service
   # sv d *
   # sv u getty*

-- Added, thanks A4L --

1. This QNAP Box runs a special flavor of Linux, so not all SOPs do apply. In my particular case I found a services.sh script, stopping all services. After that the drive could be unmounted.
2. The information passed by A4L is valid and worth reading it, maybe I'll profit from it next time. Links: http://unix.stackexchange.com/questions/19918/umount-device-is-busy and http://unix.stackexchange.com/questions/15024/umount-device-is-busy-why
3. So the unmount issue is solved, still looking for the best option to find the physical to volume mapping.