GALRU: A Group-Aware Buffer Management Scheme for Flash Storage Systems

Abstract

Many flash storage systems divide input/output (I/O) requests that require large amounts of data into sub-requests to exploit their internal parallelism. In this case, an I/O request can be completed only after all sub-requests have been completed. Thus, non-critical sub-requests that are completed quickly do not affect I/O latency. To efficiently reduce I/O latency, we propose a buffer management scheme that allocates buffer space by considering the relationship between the processing time of the sub-request and I/O latency. The proposed scheme prevents non-critical sub-requests from wasting ready-to-use buffer space by avoiding the situation in which buffer spaces that are and are not ready to use are allocated to an I/O request. To allocate the same type of buffer space to an I/O request, the proposed scheme first groups sub-requests derived from the same I/O request and then applies a policy for allocating buffer space in units of subrequest groups. When the ready-to-use buffer space is insufficient to be allocated to the sub-request group being processed at a given time, the proposed scheme does not allocate it to the sub-request group but it instead sets it aside for future I/O requests. The results of the experiments to test the proposed scheme show that it can reduce I/O latency by up to 24% compared with prevalent buffer management schemes.

Buffer Management With Append-Only Data Isolation for Improving SSD Performance

“…Page-based techniques are more suitable than blockbased techniques for increasing the buffer hit ratio or reducing the number of dirty data writes from the buffer to the NAND flash. This is because, in hot/cold prediction or clean/dirty separation of buffer entries, the accuracy of prediction/separation increases as the buffer management granularity decreases [37]. Thus, for a larger buffer management granularity, the hot/cold or clean/dirty data are more likely to be mixed within one buffer entry.…”