Solid-State Cache Management

Solid-state drives (SSDs) composed of multiple flash memory chips are often deployed as a cache in front of a cheap and slow disks [5, 2, 7]. This provides the performance of flash with the cost of disk for large data sets, and is actively used by Facebook and others to provide low-latency access to petabytes of data [3]. An SSD-backed cache, though, is limited by its narrow block interface and internal block management, both of which are designed to serve as a disk replacement [1, 8, 9]. Caches have at least three different behaviors than general-purpose storage. First, data in a cache may be present elsewhere in the system, and hence need not be durable. Thus, caches have more flexibility in how they manage data than a device dedicated to storing data persistently. Second, a cache stores data from