Novel Methods for Improving Performance and Reliability of Flash-Based Solid State Storage Syste

Though SSDs outperform traditional magnetic-based storage devices, there is still potential for further performance improvements. In existing operating systems, the software I/O stack is designed considering the working mechanisms of the traditional magnetic-based hard drives. Therefore, it has been shown that the existing I/O software layer can cause additional operational overheads for flash-based SSDs]. To address this problem, we explore the influence factors which will lead to variation of the performance of SSD. Based on our observation, we proposed a SSD-based I/O scheduler called SBIOS that fully exploits the internal parallelism to improve the performance. It dispatches the read requests to different blocks to make full use of SSD internal parallelism. For write requests, it attempts to dispatch write requests to the same block to minimize the number of the block cross requests. Moreover, SBIOS introduces the conception of batch processing and separates read and write requests to avoid read-write interference.;Besides, SSDs face reliability challenges due to the physical properties of flash memory.to fix the reliability issue of SSD, we propose a parallel and garbage collection aware I/O Scheduler called PGIS that identifies the hot data based on trace characteristics to exploit the channel level internal parallelism of flash-based storage systems. PGIS not only fully exploits abundant channel resource in the SSD, but also introduces a hot data identification mechanism to reduce the garbage collection overhead. By dispatching hot read data to the different channel, the channel level internal parallelism is fully exploited. By dispatching hot write data to the same physical block, the garbage collection overhead has been alleviated. The experiment results show that these methods significantly improve the reliability and performance of the SSD. In this research, the total number of erase operations is introduced to measure the reliability of SSD.;Meanwhile, with the rapid development of non-violate technology, due to high read/write speed, high endurance, in-place updating of PCM, many hybrid storage structures which use PCM and SSD at the same storage level have been proposed to improve the performance of SSD. However, hybrid storage systems pose a new challenge to cache management algorithms. Existing DRAM-based cache management schemes are only optimized to reduce the miss rate. On a miss, the cache needs to access the PCM or the SSD. However there are major performance differences between the access times of the two different technologies. As a result, in such a hybrid system, a higher hit rate does not necessarily translate to higher performance. To address this issue, we propose a Miss Penalty Aware cache management scheme (short for MPA) which takes the asymmetry of cache miss penalty on PCM and SSD into consideration. Our MPA scheme not only uses the access locality to reduce the miss rate, but also assigns higher priorities to SSD requests located in the page cache to avoid the high miss penalty overhead. Our experimental results show that our MPA scheme can significantly improve the hybrid storage system performance by up to 30.5% compared with other cache management schemes.