Unable to unmount drive! Somehow my harddrive seems to fail, I am not able to startup anymore. When I started in verbose mode, I noticed that the harddrive return I/O Errors and the B-Node-Tree seems to be corrupted.

I was able to use the single-user mode to backup files to an external harddrive, but when I tried to repartition the harddrive from the recovery mode, after failing to repair the partitions in single-user mode, I get an error, that he is unable to unmount the drive.

(DiskWarrior 4.4 doesn't even recognize the Macintosh HD and the S.M.A.R.T Test results are alright)

I first thought maybe something is actually used on that drive, but even after trying to repartition from the Disk Utility on a Mac OSX Lion Installer DVD, he keeps telling me, that he is unable to unmount the drive.

(I had a bootcamp partition on the harddrive as well, that is still highlighted, so that seems to be the issue)

The system is an early 2011 MBP.
Open Terminal and try entering following:

df


which will give a listing of your mounted volumes similar to:

Filesystem    512-blocks       Used  Available Capacity  Mounted on
/dev/disk0s2  1951845952 1655141456  296192496    85%    /
devfs                477        477          0   100%    /dev
map -hosts             0          0          0   100%    /net
map auto_home          0          0          0   100%    /home
/dev/disk1s2  1952853344  754604936 1198248408    39%    /Volumes/Backup


depending on which drive you need to unmount you can then try:

sudo hdiutil eject -force /dev/disk1s2


which would force /Volumes/Backup to be unmounted.