Real-time flash memory storage with Janus-FTL

Janus-FTL, a recently proposed Flash Translation Layer (FTL) software layer for flash memory storage, has the potential to reduce the worst case write time of flash memory storage by keeping hot data in the page mapping area and cold data in the block mapping area. In this paper, we present the design of the real-time Janus-FTL that guarantees worst case garbage collection cost and write response time. In the proposed FTL, each task needs to decide whether to place its data either in the page mapping area or the block mapping area. A naive optimal placement algorithm, which minimizes the worst case write time, has O(2 ^N) time complexity for N tasks. We propose an algorithm reducing the time complexity from O(2 ^N) to O(N log N). Through experiments, we verify that the real-time Janus-FTL reduces the worst case write time and, as a result, accommodates more real-time tasks than the previous state-of-the-art realtime page mapping FTL.