SSD의 병렬성과 지역성의 균형배분

Abstract

Modern flash memory based storage systems, such as SSDs (solid state disks), are actively utilizing the channel/way interleaving to exploit parallelism among multiple NAND chips. However, the flip side of the interleaving is that it disperses data with spatial locality across different NAND blocks, which eventually causes a high garbage collection overhead. To overcome this problem, we propose a spatial locality-aware allocation policy, called SLAP. It uses the notion of stream, which is defined as a set of data having consecutive logical page numbers (LBN). By allocating astream into a NAND block separately, it can preserve the spatial locality. In addition, by handling multiple streams simultaneously, it can obtain the parallelism among NAND chips. Also, we discuss that SLAP can balance between locality-preserving and parallelism by providing a spectrumfrom a traditional parallelism-oriented allocation to a strict locality-preserving one. We have implemented SLAP on a page-level mapping flash translation layer (FTL) that is being used as a default FTL in many commercial SSDs. Tracedriven simulation based experimental results have shownthat SLAP can improve performance by up to 35.3% with an average of 13.1%, compared with the traditional allocation policy for the three workload considered.es data with spatial locality across different NAND blocks, which eventually causes a high garbage collection overhead. To overcome this problem, we propose a spatial locality-aware allocation policy, called SLAP. It uses the notion of stream, which is defined as a set of data having consecutive logical page numbers (LBN). By allocating astream into a NAND block separately, it can preserve the spatial locality. In addition, by handling multiple streams simultaneously, it can obtain the parallelism among NAND chips. Also, we discuss that SLAP can balance between locality-preserving and parallelism by providing a spectrumfrom a traditional parallelism-oriented allocation to a strict locality-preserving one. We have implemented SLAP on a page-level mapping flash translation layer (FTL) that is being used as a default FTL in many commercial SSDs. Tracedriven simulation based experimental results have shownthat SLAP can improve performance by up to 35.3% with an average of 13.1%, compared with the traditional allocation policy for the three workload considered.