This is from the link I earlier provided you:It's the EHD can be usb powered or have to have a power supply cable option? (Transferring from a ViP 722 to a Hopper).
COMPATIBLE HARD DRIVES
While most major manufacturers' external hard drives are compatible with DISH DVRs, keep in mind the following guidelines when purchasing an external hard drive:
The external hard drive storage capacity for compatibility with ViP 211, 211k and 411 receivers should be between 50GB and 1TB.
The external hard drive storage capacity for compatibility with ViP 612, 622, 722, 722k and 922 receivers should be between 50GB and 2TB.
The external hard drive must have its own power supply.