DO NOT BUY A MY BOOK DUO. I have one and it has worked flawlessly, although there is one huge problem. The my book duos have a hardware encryption built into the circuit board in the enclosure. It is turned on by default and cannot be turned off. Sounds awesome right? Wrong. The encryption key for the AES-256 encryption is not provided to you and it cannot be found either. So if the circuit board fails on your enclosure you have no way to decrypt your backups on yours drives. Ohhh and simply placing the drives in a comparable enclosure does not solve the issue either
I am currently looking to get rid of mine and buy a better more effective raid enclosure. Also, WD has known about this issue for awhile and has yet to come out with either a firmware upgrade to reveal the encryption key or a way to turn off the encryption.
So I would think hard about purchasing this enclosure.