FWIW, today I tried to replace my internal drive with a Western Digital WD20EZRZ to see if it would initialize and function in the Cisco 8642. Sadly, I had NO success after 3+ hours of trying.
The 8642 sees the drive details, correctly showing 2Tb of space, but seems to be unable to initialize it with the right partition and file system(s).
I had not initialized the drive at first, but after the first failed attempt, I initialized the drive with a MBR and format a partition using EX_FAT via my windows box for some backwards compatibility in the hopes that it might spur on some progress.
The DVR did manage to remove the ex-fat partition that I had created on the drive, but not create a new one as far as I can tell.
the DVR display showed BOOT constantly. no indication ever it was formatting the drive with any hexidecimal countdown.
I suspect we really are limited to 1TB of storage.