Research On Flash File System Based On Open-channel And Dual-mode Features

With the rapid development of Internet technology,the user's demand for large-capacity and high-performance storage systems continues to grow.NAND flash memory is gradually becoming a dominant storage media due to its attractive features,such as high performance,low standby power.SSDs(Solid State Drives)making use of multiple bits per cell technology such as MLC/TLC(Multi/Triple-Level Cell)allow higher density at low prices than SLC(Single-Level Cell).However,MLC/TLC flash memory also suffers from longer read/write latency and much lower endurance compared to SLC.Existing works focus on optimizing flash translation layer(FTL)algorithm to improve system performance.However,the FTL works as a black box – its inner-workings are hidden behind a block I/O layer,for higher-level applications,the behavior of the flash memory is unknowable.It is also the biggest obstacle in reaching the full performance of the underlying flash storage.To improve the performance of flash storage systems,we design and implement a flash file system based on Open-Channel and Dual-mode features called DualFS.DualFS analyzes the source of request blocking in the storage system.With the help of the Open-Channel SSD,DualFS first uses upper-layer file system semantics to design a data management algorithm.Specifically,DualFS puts the hot data and the data with higher priority into the SLC-mode area,and uses I/O queue depth to sense the I/O intensity for reasonably allocating SLC-mode flash pages.Secondly,DualFS uses the SLC-mode write budget scheme to limit the data written to the SLC-mode area,which constrains the excessive wear caused by the SLC-mode flash blocks to ensure a balance between endurance and performance.In addition,DualFS proposes a global garbage collection strategy,which considers the Dual-mode feature and coordinates the garbage collection(GC)of the file system layer and flash translation layer to improve the efficiency of GC.DualFS uses the characteristics of SSD to reduce request delays and provides a large-capacity and high-performance storage system.Experimental results show that the throughput of DualFS is better than AMF by 22.2%.AMF is a recently proposed file system based on Open-Channel SSD.Compared with storage systems based on Dual-mode feature AMF?greedy,Ext4?comboFTL and F2FS?comboFTL,the throughput of DualFS is improved by 13.3%,24.6% and 14.0% respectively,and the erase count of flash memory is reduced by 28.0%,71.2% and 23.6%.DualFS also reduces the average read response time under different read/write ratios.