2QW-Clock: An Efficient SSD Buffer Management Algorithm

Modern solid state disk (SSD) has a buffer (SDRAM), which is used to store commonly used data and map in the near future. How to efficient management of this buffer is an important things of improving performance of SSD. Flash read and write speed have asymmetric characteristic. SSD buffer management algorithms must consider this characteristic of flash. Current page mapping SSD buffer management algorithms mainly use the Clean-First LRU (CFLRU) algorithm to first replace the clean buffer pages regardless of whether these pages will soon be used in the near future. At the same time, LRU buffer management algorithm of SSD does not consider file scanning. In order to solve these problems, we proposes a new SSD internal buffer management algorithm, called Two Queue Weight-Clock (2QW-Clock). This algorithm combines the advantages of 2Q and gives different weights to read page and write page to reflect the asymmetry of flash read and write speed. Therefore, it can get high write page hit ratios while maintaining high total page hit ratios. With the high write ratios, 2QW-Clock reduces the numbers of SSD write and erase operations. So it can greatly extend the life of the SSD. Conducting simulations with a variety of traces and a wide range of buffer sizes, we show that 2QW-Clock write hit ratios are significantly higher than CFLRU, LRU and 2Q in most cases while total hit ratios are almost as the 2Q. Simulation result shows that the numbers of 2QW-Clock write and erase counts reduced by up to 30% less than that of 2Q and CFLRU.