I apologize if this question has been addressed in another thread. I did some searching and found part of my answer but not all of it.
I have an HR21-PRO that I'm 99% certain has a failing HDD. I actually have two (2) HR21-PROs in my system and having two of them provides significant more diagnostic capability. For example, if one unit works fine and the other does not, it can't be or is not likely to be a dish-aiming or other input signal issue.
I gathered from other threads that these units will work with a brand new HDD installed without any sort of formatting or installation of an OS on the drive. Apparently, these DVRs have all necessary boot-up info and OS in firmware, unlike a PC where the OS must be installed on the HDD before you can use the machine.
My remaining question is simply: The HR21-PRO comes with a 500GB HDD. Can I install a 1TB or even 2TB HDD and expect it to work? I guess I'm concerned about the unit recognizing and being able to use a larger drive.