Is it possible to use a sd card to act as a non volatile cache for a hdd in a mobile cctv dvr.
This is to stop the loss of data in the cache of the hdd if the drive fails or power is lost from vehicle ie. in a heavy impact collision.
Can this non volatile memory be backed up by a battery.

I don't know about using flash as a non volatile cache, but if you're expecting heavy impacts, an SSD drive, eliminating a conventional drive, may be the way to go. If the drive size is large enough, there likely won't be enough writes to shorten it's life much.

Thanks for that and yes I agree a large capacity ssd drive would be perfect but they just cost so much.

All I need is a bit of solid state in line with the standard drive so I will always have the last few minutes footage no matter what happens to the hdd.

Does anyone know if there is a way of using 2 drives -1.32gb ssd and 1.250gb hdd together without Raid as I do not want to lose the capacity of the 250gb hdd.

Are there any ways to cheat/trick a Raid array?

The only thing I can think of would be to mirror, take say a 32GB SSD, cut the hard drive to the same size, and everything will go to both. Of course, you still have the problem with the SSD price, and you don't really need the HD. 'Tricking' a RAID to do something else just sounds scary. I'm assuming you had some hardware-based DVR. If it's a PC, you might have some more options. It really depends on your hardware, software, OS, etc.. Also, it depends on how long you need to record. Maybe a 4GB or 8GB SD card would work in your application, and even be cheaper than a drive.

Is there a magic box that plugs into an IDE connector that can do what you want? Likely no. It's possible it can be made, but that will be very expensive, impractical, and likely completely unnecessary. Share some more hardware/software details, and the project requirements, and you might get some better help.

Also, add your project's price requirements. You might be fighting over nothing.