The traditional solid-state drive buffer management algorithm generally adopts fixed structures and parameters, leading to their poor adaptability. For example, after the underlying flash translation layer (FTL) or the upper workload is changed, the traditional algorithm's performance fluctuates significantly. Focusing on this problem, based on the cross-layer aware method, we propose an Advanced Adaptive Least Recently Used buffer management algorithm (AALRU). The core idea of the AALRU is that by sensing the characteristics of the upper workload and the status of the underlying FTL, the AALRU adaptively adjusts its structure, parameters, and write-back strategy to optimize the buffer's performance. First, the AALRU divides the buffer into two parts: read buffer and write buffer, and their proportion is adjusted by sensing the read-write characteristics of the workload and the underlying read-write latency. Second, the AALRU employs different granularities to manage the buffer. On one hand, for data loading and migrating, the AALRU adopts page-level granularity, which can avoid the problem of hot and cold data page entanglement in block management, and thus improve the buffer hit ratio. On the other hand, for data writing back to the FTL, the AALRU adopts block-level granularity, which can enhance the continuity of write requests and thus reduce the underlying FTL's garbage collection overhead. Finally, when the clustered data are written back, by sensing the underlying FTL's garbage collection status, the AALRU adaptively adjusts the page-padding trigger threshold to reconstruct the continuity of the write-back data, which can mitigate the underlying FTL's garbage collection overhead. The experimental results show that the AALRU has the best adaptability to different FTLs and test workloads, and it can achieve optimal or near-optimal results. INDEX TERMS Solid-state drive, buffer management, adaptive algorithm, cross-layer aware. I. INTRODUCTION The performance of processors has increased rapidly in accordance with Moore's Law over the past few decades. However, the performance improvement of a storage system based on a hard disk drive (HDD) has been slow, which has led to an increasing performance gap between computing and storage [1]. Compared with the traditional HDD, the solidstate drive (SSD) based on the NAND flash memory has many excellent features such as its low power consumption, fast reading and writing speed, light weight, small size, shock resistance, and noise-free performance [2], [3]. The associate editor coordinating the review of this manuscript and approving it for publication was Guan Gui.
The classic demand-based flash translation layer (DFTL) algorithm is well-known since it can solve the contradiction between mapping flexibility and the size of mapping cache by dynamically loading mapping entries. However, DFTL failed to utilize the spatial locality and hot-cold characteristics of the request and had an inefficient mapping entry eviction scheme. This paper proposes an adaptive readwrite partitioning flash translation layer algorithm (ARWFTL). First, the cache mapping table (CMT) is divided into the read CMT and the write CMT. The size of the two can be adaptively adjusted by sensing the characteristics of the upper workload and the read-write latency of the underlying flash page. Second, a priority eviction window is set at the tail of the write CMT to evict the clean mapping entry firstly. When there is no clean mapping entry in the priority eviction window, the tail mapping entry and other mapping entries that belong to the same translation page are clustered to write back into the translation page. Then, other written back mapping entries are set to be clean and the tail mapping entry is evicted. Third, a hot data window is set at the head of the write CMT to recognize the hot and cold data of write requests. Then, the hot and cold data are stored in different data blocks of flash to avoid hot and cold data entanglement and reduce valid page migrations in garbage collection. Experimental results show that, compared with DFTL, ARWFTL can reduce the translation page write counts, the valid page migration counts, the block erase counts, and the average response time by 92.8%, 47.7%, 31.7%, and 31.4%, respectively. In addition, ARWFTL is also superior to the other recent DFTL-based improved algorithms, and even exceeds the pure page-level FTL in some indicators. INDEX TERMS Solid-state drive, flash translation layer, adaptive read-write partition, cache mapping table. MINGBO YAN received the B.E. degree in communication engineering from Hangzhou Dianzi University, China, in 2017, where he is currently pursuing the M.E. degree. His current research interest includes storage system design with solid state drive. XIAOCHONG KONG received the B.E. degree in communication engineering from Hangzhou Dianzi University, China, in 2018, where he is currently pursuing the M.E. degree. His current research interest includes storage system design with solid state drive. XIAORONG XU received the Ph.D. degree in signal and information processing from the Nan
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