I have just read an article on installing a ingle wd purple hdd in one of these units. He said he initialized the drive and it started recording but still beeps as it says missing drive for the other side. Do you have to have 2 drives or can you stop it beeping with only 1 drive?
After installation of the drive you just go to Storage Management, tick the box for the installed drive and select initialise - that's it. You don't have to populate it with two drives.
If you can see one drive that you know is physically there and it's showing "missing" for the other, that would indicate that there has been a drive connected at some point. Is this a brand new NVR or second hand?
You can select the drive that says "missing" and...