I've been having lot's of problems getting my MBWE working, but eventually managed to get the SSH mod installed, found lot's of errors on the drive, fixed them, but still only seemed to have a very small amount of disk space available.
On running mount to see what was happening I discovered that the main disk partition /dev/md4 was not mounted.
When I tried to mount it manually I like several others, got the error message -
mount: Mounting /dev/md4 on /shares/internal failed: Invalid argument
I checked in /etc/fstab and everything seemed to be in order there, tried a few variations , just in case but nothing seemed to cure this problem.
but I discovered that if I mount it by using
Mount /dev/md4 /shares/internal
I eventually realized that the problem was caused by /dev/md4 having somehow lost it's journal file so becoming an ext2 partition instead of a ext3 so refusing to mount as the filesystem did not match that specified in /etc/fstab
I ran tune2fs -j /dev/md4 to create the journal and lo and behold everything now works!