I want to add an external Hard Disk?

You would simply enter the IP address of your Humax into a Telnet client e.g. Putty, this will attempt to login to your Humax using the default Telnet port of 23
So it seems I'll have to use ext2/3 file format (never heard of it before) - and I'll have to use a utility to allow me to "mount" the drive. Hmmm again.
That's only if you want to read the data with a Windows PC. If you are happy to dedicate a drive to backup storage for your HDR, use the HDR menus to format it (Ext3) and then you can write and read to it from the Humax with no hinderance.

Seagate 1TB portable drives (USB3 - but it works) are currently available from PC World for £55.
Well installed the CFW, and reports "Disk Overall Health - Failed" - indicating a failing disk. So all recordings will be copied off as soon as my external HDD arrives. Meantime I'll see if I cant use the disk utilities via telnet to fix it.....