The magic number right now is 2.1TB
. The dock shouldn't care about this limit (it just passes instructions and data back and forth between the drive and the computer), but your operating system needs special support to handle individual drives over 2.1TB:
The problem is that not every OS supports Long LBA, and Seagate says this includes any 32-bit operating system, including Windows XP. In fact, Seagate says that its own tests have shown that a 3TB drive is only detected as a 990GB drive when using Windows XP. On the plus side, the 64-bit versions of Windows Vista and Windows 7 support Long LBA, as do some versions of Linux and Mac OS X.
This means things won't work right if you try to stick a 3TB drive in any dock if your OS doesn't support it.