How do I attach an external hard disk to my HD DVR to expand storage?

Some SATA drives work and others don't so just be warned.   I have an SA8240 and the second attempt I made to try this wiped everything off my DVR.  Here's the link to the user's manual for your DVR.  The instructions are on pg. 17 along with the specs for the HD that are recommended.

http://media.cox.com/support/print_media/tv/equipment/user_guides/cable_box/SA8300HDC_user_guide.pdf

I tried this several times and the instructions for formatting the HD only appeared when the HD became partially unplugged.  When I pushed the eSATA cable back into the docking station the message to format the HD finally appeared.  The drive I use is a Seagate Barracuda 1TB 7200 rpm Black.  I've also seen on some websites that the WD Cavair black drives also work.  I also use a Thermaltake docking station