I am of the opinion that it depends on which version of the software you are running, and quite possibly, which drive you happen to choose. There's a big thread @ AVS here on the subject. Keep in mind that most cable companies do not have this feature. If you want the most reliable solution, rent the larger capacity DVR.
I've read some of the old posts on the High Def Forum about this topic but it still seems confusing and no one, including Cox (Phoenix, AZ), is willing or able to give me a straight answer. I have a SA Explorer 8300HD DVR and want more storage space. I am running Passport ECHO version 3.1.085 and PowerTV version 184.108.40.206sp. Cox tells me that I should be able to use eSATA but they won't recommend any particular brand and they won't give tech support. I'm not into building an external hard drive. What I want to do is go to Best Buy, buy a 1TB external drive, and hook it up. So, what I want to know is what are my chances of this working? If there's a good chance that it will work is there any particular brand I should get and any specs that I should look for? My other alternative is to swap my current box for an updated version with more storage but then I will lose any currently recorded programs. Any help is appreciated.