Multi-level RAID for very large disk arrays

  • Authors:

  • Alexander Thomasian

  • Affiliations:

  • New Jersey Institute of Technology, Newark, NJ

  • Venue:
  • ACM SIGMETRICS Performance Evaluation Review - Design, implementation, and performance of storage systems
  • Year:
  • 2006

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Abstract

Very Large Disk Arrays - VLDAs have been developed to cope with the rapid increase in the volume of data generated requiring ultrareliable storage. Bricks or Storage Nodes - SNs holding a dozen or more disks are cost effective VLDA building blocks, since they cost less than traditional disk arrays. We utilize the Multilevel RAID - MRAID paradigm for protecting both SNs and their disks. Each SN is a k-disk-failure-tolerant kDFT array, while replication or l-node failure tolerance - lNFTs paradigm is applied at the SN level. For example, RAID1(M)/5(N) denotes a RAID1 at the higher level with a degree of replication M and each virtual disk is an SN configured as a RAID5 with N physical disks. We provide the data layout for RAID5/5 and RAID6/5 MRAIDs and give examples of updating data and recovering lost data. The former requires storage transactions to ensure the atomicity of storage updates. We discuss some weaknesses in reliability modeling in RAID5 and give examples of an asymptotic expansion method to compare the reliability of several MRAID organizations. We outline the reliability analysis of Markov chain models of VLDAs and briefly report on conclusions from simulation results. In Conclusions we outline areas for further research.