Expensive solution - This should be done at the drive level
The major drive mfgs can place 4/8/16 Gig flash units on individual drives. These can act as read/write buffers with automatic data recovery after a power failure (if any). 16Gig should be more than enough to take care of background (lazy) writes and speed up overall performance at the individual drive level. An array of these drives can then be setup without the need for another front end box.