A Cache Scheme For Improving Random Write Performance In SSD

Compared with CPU rate accelerating and network bandwidth increasing, the development of storage devices can not keep up with the development of them fully, so that, storage devices have become one of the bottlenecks in the process of computer systems'development. With the continuous growth of information, information processing rate is demanded for improving continuously, so that, the bottleneck becomes more and more obvious and mechanical hard disks are unable to meet the requirements. The appearance of Solid State Disks which are semiconductor-based have injected new vitality into storage industry. SSD has become the most important storage device in portable devices, and will replace HDD gradually in desktop devices.SSD has various advantages over HDD, such as fast IO speed, low power consumption, high reliability, etc. But SSD also has disadvantages for its inherent characteristics, such as unbalance of IO, erase-before-write and so on. These disadvantages cause poor performance of random write, and they obstacle the application on the desktop environment seriously.In order to improve the random write performance of SSD, the mapping algorithm and garbage collection(GC) algorithm in FTL have been studied. We add cache layer on top of FTL layer, organize random data into sequential data in cache layer and then write them into FTL layer. In addition to effectively improve the random write performance, this method can also reduce erase operation, to extend the life of SSD.Simulation to test this cache algorithm, and the results show that write throughput improved and erase operation reduced significantly. In addition, this cache algorithm is better than FAB in real applications.