FireStore - which are generally firewire connected to miniDV tape based camcorders' DV port, Sony has the external HVR-MRC1K compact flash storage unit and HVRDR60 hard disc drive unit... both are also connected to the camcorder with firewire and record to DV/HDV video formats like the camcorders to which they are connected do.
I am not aware of any HDMI-connected external hard drive camcorder storage devices.
Since you did not tell us which camcorder you are wanting to connect this external device to, any other additional research is a challenge.
I was wondering if there were any other systems like FireStore FS-4 or FS-100 out there, other than the FireStore ones?
I'm trying to see if I can output the sensor signal from the HDMI-out on my camera and have it go to an external DTE device, but I don't like the FireStores that much.