A Real-Time Dependable Flash Storage System

Abstract

One of the limitations of flash memory in real-time and high dependability systems is its need for garbage collection, resulting in performance degradation due to non-deterministic response times. Recent work has presented RAID architectures for solid state storage systems. These RAID architectures increase the dependability from a data storage perspective but they do not provide application level dependability when real-time response times are required. In this study we present a garbage collection aware Flash Translation Layer that offers guaranteed access time to a solid state RAID array by managing incoming requests and preventing them from being blocked by ongoing garbage collection. We present a novel serial technique with a dynamic page allocation mechanism that eliminates non-deterministic behaviours of the garbage collectors in the array. The result is real-time access guarantees that maintain the data dependability enhancements using a run time parity migration technique. The mechanisms are evaluated using a trace driven simulator and a number of synthetic and realistic traces. Simulation results indicate that the garbage collection aware techniques offer improved upper bound response times for I/O requests of up to 73% compared to an existing mechanism, without disturbing the data dependability at the storage level. Traces dominated by random writes exhibit similarly significant enhancements.INDEX TERMS Data storage systems, flash memories, fault tolerance, flash translation layer, garbage collection, real-time systems, SSD RAID.