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.