Amazon (AWS) Import Export Service: Supported Devices.

313goaf9WHL._SL75_Generally a line of external drives from LaCie, MicroNet, Seagate, and Western Digital are supported.

Since they claim 16TB is the maximum volume size, I recommend something like this one from Lacie:

 

http://aws.typepad.com/aws/2010/03/aws-importexport-support-for-raw-drives-and-bigger-devices.html