CPR for SSDs

Modern storage systems are built upon the assumption that the capacity of a storage device does not change. This capacity-invariant interface forces a flash-based storage device to trade performance for reliability when, in fact, it can maintain both if a graceful reduction in capacity were to be allowed. We argue that relaxing the fixed capacity abstraction of the storage device allows for a better capacity-performance-reliability (CPR) tradeoff. We then outline existing device-internal mechanisms for building a capacity-variant flash device, and describe the necessary changes in the storage stack.