Buy multiple cards for each camera, rotate each card for each camera over 7 days, so each card becomes a backup in its own right. This was typical for tape data storage not that long ago, often rotating 30 tapes every 30 days, so 30 backups. So 7 cards per camera. You really should have 2 cameras per side of car. I have skimped a bit with 1 camera per side but at least 2 cameras for redundancy in the front. I have a second camera for the rear but currently I am using it for a live feed for rat traps in our roof, they keep eating the electrical wires. My understanding is that the largest hard drive to go for is 2GB as beyond that the hard drives use multiple platers, less reliability. Do a backup hard drive for each camera off site just in case of a fire with 7 years back up for legal requirements. Just in case, a second back up on another continent just in case of a meteorite strike or Chinese failed space station orbital failure. Not to forget automatic hot power switching just in case your power supply fails, the thing you would do for any mission critical computers. I had this for blackouts for 3d rendering for computers. Nothing pis_es you off more than a 12 hour 3d computer render & a blackout minutes before the end!
Or you could buy the largest card the camera will utilise. If it's 512MB you should get up to about 100 hours before rewriting at a lowish resolution & simply let & forget, & second camera for redundancy which would covers most levels of failure.
