A highly reliable storage based on SSD array for cloud computing environment

Abstract

As Solid State Drives(SSDs) have becomemore cost effective, they are widely used from embeddeddevices to enterprise storage systems. However, they have typical problem called write amplificationwhich is caused by out-of-place updates characteristicsof NAND flash memories. As the write amplificationincreases, it degrades I/O performance andreduces lifetime of SSDs. When using SSDs in a paritybased RAID, parity updates amplify these performancedegradations. This paper presents a method to reducewrite amplification problem of SSDs in a parity basedRAID. To solve this problem, we propose a new parityupdate scheme, called LPUS. LPUS transforms randomparity updates to sequential log writes with additionallog blocks in SSD arrays. In contrast to the conventionalparity update scheme, our approach reduces the blockfragmentation by using parity logs and the number ofparity updates by updating parities in a lazy manner. The experimental results show that, LPUS reduceswrite amplification up to 37% and the number of eraseoperations up to 50% with the reasonable size of log space.