I have a drive which I used to use as a backup drive on this computer. I removed it prior to upgrading from 11.10 to 12.04 because I was also installing a new GPU which was too big and the extra drive wouldn't fit.
Well now a client is reporting a bug on some 2 year old software I wrote and the sources are on this drive. So I plugged it back in and now, of the two partitions on it, only one will allow me to view/edit the files. The other says there is X amount of data being used but I cannot see anything on the drive.