Research On SSD-Based RAID Mechanism

Data-intensive applications increasingly demand a high-performance and highly reliable storage system. Hard disk drive (HDD) has long been used as a standard storage device for most existing storage systems, but HDD can hardly meets performance and reliability requirements of data-intensive applications. Recently, NAND-flash memory based solid state drives (SSDs) are gradually exploited to replace HDDs in storage systems due to their salient features such as high performance, low power consumption, and excellent shock resistance. With rapid price decreasing and capacity increasing, flash SSD based disk arrays organized in some RAID (Redundant Array of Independent Disks) structures become feasible and greatly needed.This thesis makes research on RAID mechanism in storage system based on SSDs (Solid State Drives). Firstly, we analyze and compare different RAID mechanisms used on SSDs. Secondly, we propose a new RAID4 architecture called SPD-RAID4 (Splitting Parity Disk-RAID4) for parallel SSD (Solid State Drive) arrays. It splits the parity disk of a traditional RAID 4 array into configurable number of smaller ones. Thus, multiple small parity SSDs operate in tandem with data SSDs to achieve a high performance and high level of reliability. Thirdly, in order to compare performances between multiple RAID architectures, we developed an SSD RAID simulator that can simulate standard RAID4, RAID5, and SPD-RAID4, we call it SSDsim_for_RAID. Our simulator is built based on a validated single SSD simulator called SSDsim developed by Hu et al. Lastly, we compare the performance of SPD-RAID4 with conventional RAID4 and RAID5 architectures by using both real-world traces and synthetic benchmarks. Experimental results demonstrate that in terms of mean response time SPDRAID4 outperforms standard RAID5 structured SSD arrays by up to 20.3%. Compared with standard RAID4, SPD-RAID4 achieves a performance gain up to 40.6%.