Modern AV drives (WD Purple, Seagate Skyhawk) have firmware which is optimized for continuous write operations from multiple camera inputs. It's important to record all the information from the cameras and not drop occasional frames when outputting data or performing housekeeping tasks. As such, I don't think the hard disk in your Humax recorder qualifies as a "video" drive. Large capacity drives (8TB and above) often have larger cache sizes of 256 or 512MB, so they're not unique to video drives.
I've just removed the lid from my mother's old Panasonic DMR-EX77 Video/DVD recorder which I'm supposed to be fixing and the disk inside is a 160GB Hitachi Deskstar 7,200rpm ATA/IDE drive, date code May 2007, part number HDS721616PLAT80.
It's most definitely not SATA, but has a very fine ribbon cable leading up to a small PCB header, which interfaces with the standard 40 pin connector on the 3.5" hard disk drive.
I've been considering replacing the drives in several of these Panasonic recorders, but I have no idea if their equivalent of a BIOS will support drives larger than 160/250GB. Even if I could find a suitable 1TB IDE drive in my junk pile, the "BIOS" might refuse to recognise it.
The 160GB "Deathstar" drive is marked LBA 321,672,890 sectors, C/H/S 16383/16/63. Since it supports Cylinder/Head/Sector addressing, there may be a limit I can no longer remember that precludes really big drives.
I believe I'd need to perform a bit-by-bit copy of the drive and just I hope the likes of Macrium Reflect can cope with the non-Windows proprietary format used by Panasonic. There might even be some form of copy protection or encryption incorporated in the design, making it impossible to get the cloned drive to work in the recorder. No doubt the AV forums would help.
My solution to the lack of recording on the DMR-EX77 (it still plays back fine off hard disk) was to buy a brand new Panasonic DVD/hard disk recorder for my mother. She's got used to the old interface and the function of the remote control buttons, so she wouldn't thank me for providing a new-fangled "modern" device. She has however mastered the art of booting up Hyper-V images on her desktop computers.
If you cannot find information on your Humax recorder online, you'll just have to find someone reliable to untangle and disconnect all the wires from the back of the machine and place it on a workbench. Best of luck with the upgrade.