Physically addressed queueing (PAQ): improving parallelism in solid state disks

  • Authors:

  • Myoungsoo Jung;Ellis H. Wilson, III;Mahmut Kandemir

  • Affiliations:

  • The Pennsylvania State University;The Pennsylvania State University;The Pennsylvania State University

  • Venue:
  • Proceedings of the 39th Annual International Symposium on Computer Architecture
  • Year:
  • 2012

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Abstract

NAND flash storage has proven to be a competitive alternative to traditional disk for its properties of high random-access speeds, low-power and its presumed efficacy for random-reads. Ironically, we demonstrate that when packaged in SSD format, there arise many barriers to reaching full parallelism in reads, resulting in random writes out-performing them. Motivated by this, we propose Physically Addressed Queuing (PAQ), a request scheduler that avoids resource contention resultant from shared SSD resources. PAQ makes the following major contributions: First, it exposes the physical addresses of requests to the scheduler. Second, I/O clumping is utilized to select groups of operations that can be simultaneously executed without major resource conflict. Third, inter-request NAND transaction packing empowers multi-plane-mode operations. We implement PAQ in a cycle-accurate simulator and demonstrate bandwidth and IOPS improvements greater than 62% and latency decreases as much as 41.6% for random reads, without degrading performance of other access types.