ShiftFlash: Make flash-based storage more resilient and robust

Abstract

Flash based storage technology has been steadily gaining more and more popularity during the past decades due to its unique merits over conventional disk counterparts and has been projected to revolutionize the entire storage hierarchy. Though it is well-known that flash storage is physically more reliable than hard disk drives within its limited lifespan, neither of them provide sophisticated built-in mechanisms guarding against non-physical failures, such as virus attacks and unintentional errors. One of the unique characteristics of flash is “no in-place overwrites”, which would cause a large amount of superseded pages/data to remain in the flash until they are selected to be erased by a garbage collection process. Leveraging this idiosyncrasy, we propose ShiftFlash, which provides flash based storage with time-shifting functionality to make it more robust and resilient. By monitoring and recording the modifications of the FTL mapping table, ShiftFlash enables flash state to be reverted to any point-in-time (PiT) in the past. It is implemented within SSD devices and needs minimal support from the upper layer. The trace-driven simulation results of a range of different workloads show that ShiftFlash only introduces marginal overheads with respect to several principal performance metrics, somewhere between 6% and 11%, compared with the original non-shifting flash. ShiftFlash also outperforms other time-shifting schemes by a large extent in many respects.