dipkiwi:3.5" 1 TB WD Elements Model
Like I say... a powered external hard drive is different to a USB powered storage device.
I run a Verbatim USB 500GB hard drive with no issues whatsoever.
http://www.jbhifi.co.nz/computers/storage/verbatim/500gb-portable-hard-drive-sku-21721/
The WD Elements drive IS a powered external hard drive, and the problem I experienced trying to use it on a 980HD may not occur with drives of other makes (since some are said to work) or on other PVRs.