The HDRs aren't intended for long-term storage, and as the OP's was come by cheap, shouldn't be relied on for such.
In his position, I'd leave the 500GB drive installed, package a suitable 1TB drive in a USB enclosure and attach externally to supplement the storage/archive programmes in a way they can be viewed elsehow should the HDR fail.
In his position, I'd leave the 500GB drive installed, package a suitable 1TB drive in a USB enclosure and attach externally to supplement the storage/archive programmes in a way they can be viewed elsehow should the HDR fail.