Directv DVR and external portable Hard Drive

No, it won't. If you have one of the HD DVRs with Esata you can connect an external drive that will be used in place of the internal drive. They cannot be used together.
Alternatively, you can upgrade the internal drive. You cannot use the USB port for drive connectivity.

How do I know if I have Esata? What do I look for?

Thanks

check the video forums - there's a tremendous amount of info on this topic. the (Comcast) Scientific Atlanta SA 8000 HD is said to use the internal and external at the same time. You do have to use the esata connection. Western Digital makes an external esata hd specifically for the the S.A. box. Supposedly av hard drives are a little different from standard computer external data drives, they stream the data with fewer interruptions.

Yashu, if you have the HR20 or 21 series there is a esata connection.