Largest HD Size on ReadyNAS Duo V2

I'm not sure where you are getting that information. JohnCM_S, but I would expect a Netgear moderator to have his facts straight. The DuoV2 absolutely can support drives >4TB. I put 6TB's in one and it worked just fine.  The original documentation only lists 4TB because nothing bigger existed at the time. There may be a limit in the firmware of the volume size, but I know it's at least 12TB.  If there is a real hard limit, please get your facts straight and post it.

Now, with the slow processor and small memory of the DuoV2, there is perhaps a practical limit, especially with multiple users. But used by a single user where speed is not critical (like as a backup device for a computer a newer NAS), a bigger volume certainly is a viable option.

As far as the hardware compatibility list goes, it is woefully out of date. It even lists drives like the WD Caviar Green and Seagate Baracude DM and DL drives that are very poor choices for a NAS (at least when part of a RAID array)..