Non-volatile storage technologies such as flash memory, Magnetic RAM (MRAM), and MEMS-based storage are emerging as serious alternatives to disk drives. Among these, MEMS storage is predicted to be the least expensive and highest density, and at about 1 ms access times still considerably faster than hard disk drives. Like the other emerging non-volatile storage technologies, it will be highly suitable for small mobile devices but will, at least initially, be too expensive to replace hard drives entirely. Its non-volatility, dense storage, and high performance still makes it an ideal candidate for the secondary storage subsystem. We examine the use of MEMS storage in the storage hierarchy and show that using a technique called MEMS Caching Disk, we can achieve 30-49% of the pure MEMS storage performance by using only a small amount (3% of the disk capacity) of MEMS storage in conjunction with a standard hard drive. The resulting system is ideally suited for commercial packaging with a small MEMS device included as part of a standard disk controller or paired with a disk.