Preemptible I/O Scheduling of Garbage Collection for Solid State Drives

Journal Article · Sun Jan 01 00:00:00 EST 2012 · IEEE Transactions on Computer-Aided Design of Integrated Circuits and Systems

OSTI ID:1061554

Lee, Junghee ^[1]; Kim, Youngjae ^[1]; Shipman, Galen M ^[1]; Oral, H Sarp ^[1]; Kim, Jongman ^[2]

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1. ORNL
2. Georgia Institute of Technology

Abstract Unlike hard disks, flash devices use out-of-update operations and they require a garbage collection (GC) process to reclaim invalid pages to create free blocks. This GC process is a major cause of performance degradation when running concurrently with other I/O operations as internal bandwidth is consumed to reclaim these invalid pages. The invocation of the GC process is generally governed by a low watermark on free blocks and other internal device metrics that different workloads meet at different intervals. This results in I/O performance that is highly dependent on workload characteristics. In this paper, we examine the GC process and propose a semi-preemptible GC scheme that allows GC processing to be preempted while pending I/O requests in the queue are serviced. Moreover, we further enhance flash performance by pipelining internal GC operations and merge them with pending I/O requests whenever possible. Our experimental evaluation of this semipreemptible GC scheme with realistic workloads demonstrate both improved performance and reduced performance variability. Write-dominant workloads show up to a 66.56% improvement in average response time with a 83.30% reduced variance in response time compared to the non-preemptible GC scheme. In addition, we explore opportunities of a new NAND flash device that supports suspend/resume commands for read, write and erase operations for fully preemptible GC. Our experiments with a fully preemptible GC enabled flash device show that request response time can be improved by up to 14.57% compared to semi-preemptible GC.

• Research Organization: Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). National Center for Computational Sciences (NCCS)
• Sponsoring Organization: USDOE Office of Science (SC)
• DOE Contract Number: DE-AC05-00OR22725
• OSTI ID: 1061554
• Journal Information: IEEE Transactions on Computer-Aided Design of Integrated Circuits and Systems, Vol. 32, Issue 2
• Country of Publication: United States
• Language: English

Related Subjects

Storage Systems
Solid-state Drives (SSDs)
Flash Memory
Performance Evaluation
Garbage Collection
I/O Scheduling