take one of those cards with sata interface and DDR2 ram put it in raid array. horray.
Storing on flash memory is better if you don’t write too much.
That memory is pretty short lived when you have to do that sort of operations. IIRC, the MTBF for each bits is around 100k writes.
That makes much when you write some mp3s from time to time and pass most of the time reading them, but for a swap/HD replacement, you’d avoid it at all costs.