Are you using DSM 4.2? I don't think I had an issue connecting up my Mac formatted HFS+ drive in an USB 3 enclosure to the USB port on my DS212j... but it has been awhile. I recall being surprised because I though it was going to ask to reformat it. I just had to set permissions if I recall correctly... hmmm... I can use the drive for TM backups, but that may just be a server thing.