I was going to mention this earlier (2 years ago!) - the VMS1110 did recognize the external HDD but I didn't know whether or not the capacity increased. The problem was I plugged in my HDD and a seemingly new DVR show listing file was created because all my shows on the DVR went unlisted. This scared me so I turned off the VMS and unplugged the HDD. Fortunately, the DVR shows were listed again when the VMS restarted. I have been meaning to watch and delete all my programs but the DVR has stayed 90%+ full for the past two years.
If you have a new VMS1100 or don't care about the shows on your DVR, turn off the VMS and plug in the HDD. If you did have shows recored previously, see if they are gone after the VMS restarts. If so then at least you can tell the HDD is recognized by the VMS. Either way, record a few HD shows and see if the percent recorded indicates the DVR capacity is ~160 hrs (1TB) or ~320 hrs (2 TB) of HD video.
Right now my DVR (1TB) has 155h 45m of HD programming at 92% full as shown on the DVR menu (configure & upgrade -> check capacity). That's about (155.75 hrs / .92 😃 169 hrs total capacity on my VMS. If you get double than that then the HDD works! Let us know!
As was the case two years ago, my DVR stays near full. The other DVR that my wife uses constantly stays full and autodeletes the oldest shows as necessary. It would be nice to have double the capacity especially because my HDD has just been sitting in a drawer for the past two years except when I tried plugging it in that one time.