The Netezza database appliance essentially works like this -- each disk is paired with an FPGA and a CPU core. The disk-local CPU takes care of caching directory information for the disk, decides what order to process disk pages in, and manages a disk cache with full awareness of the application. After a disk read the FPGA cuts away unwanted data before the CPU has to look at it. This has been shipping for several years.

To the extent that your problem is embarrassingly parallel and can be executed near the disk, you speed up linearly with the number of disks.

(I am currently employed by Netezza)