NAND flash memory -- the stuff of which solid-state drives are made -- is up to 1,000 times faster than disk storage and many times cheaper than DRAM. Flash memory is the hottest commodity in storage, and it will be even hotter when storage management software catches up with the potential of flash in the data center.
Flash memory's special combination of high speed and low cost makes it an excellent choice for server-side cache, where it replaces pricier DRAM, and the natural choice for tier-one storage in SANs, where it replaces slower disks. With the cost of flash steadily dropping and the capacities of SSDs steadily on the rise, the days of disk drives in servers and SANs appear to be numbered.
The best part: Having flash storage in servers introduces a possibility that simply wasn't practical with disk -- namely, managing server-side storage as an extension of the SAN. In essence, server-side flash becomes the top tier in the SAN storage pool, drawing on intelligence within the SAN to store the most frequently accessed or most I/O-intensive data closest to the application. It's like caching, but smarter and more cost-effective.
The huge performance advantages of flash have made automated tiering within the SAN more compelling than ever. All of the leading SAN vendors now offer storage systems that combine solid-state drives, hard disk drives, and software that will dynamically migrate the "hottest" data to the fastest drives in the box. The next step will be to overcome the latency introduced by the distance between SAN and servers. The speed of flash and block-level autotiering software -- which operates in chunks as fine as kilobytes or megabytes -- will combine to close this last mile.