OK I think I narrowed my problem down to this line:

/dev/mmcblk0p2 on /home

Could somene a bit more learned in linux please confirm that this is not the n900s own internal storage before I attempt to unmount this. Also, will the command "unmount /dev/mmcblk0p2 " do the trick?

The full text of the line as it appears when the mount command is entered is:

/dev/mmcblk0p2 on /home type ext3 (rw,noatime,errors=continue,commit=1,data=writebac k)