The pitfalls of deploying solid-state drive RAIDs

  • Authors:

  • Nikolaus Jeremic;Gero Mühl;Anselm Busse;Jan Richling

  • Affiliations:

  • University of Rostock, Germany;University of Rostock, Germany;Berlin University of Technology, Germany;Berlin University of Technology, Germany

  • Venue:
  • Proceedings of the 4th Annual International Conference on Systems and Storage
  • Year:
  • 2011

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Abstract

Solid-State Drives (SSDs) are about to radically change the way we look at storage systems. Without moving mechanical parts, they have the potential to supplement or even replace hard disks in performance-critical applications in the near future. Storage systems applied in such settings are usually built using RAIDs consisting of a bunch of individual drives for both performance and reliability reasons. Most existing work on SSDs, however, deals with the architecture at system level, the ash translation layer (FTL), and their influence on the overall performance of a single SSD device. Therefore, it is currently largely unclear whether RAIDs of SSDs exhibit different performance and reliability characteristics than those comprising hard disks and to which issues we have to pay special attention to ensure optimal operation in terms of performance and reliability. In this paper, we present a detailed analysis of SSD RAID configuration issues and derive several pitfalls for deploying SSDs in common RAID level configurations that can lead to severe performance degradation. After presenting potential solutions for each of these pitfalls, we concentrate on the particular challenge that SSDs can suffer from bad random write performance. We identify that over-provisioning offers a potential solution to this problem and validate the effectiveness of over-provisioning in common RAID level configurations by experiments whose results are compared to those of an analytical model that allows to approximately predict the random write performance of SSD RAIDs based on the characteristics of a single SSD. Our results show that over-provisioning is indeed an effective method that can increase random write performance in SSD RAIDs by more than an order of magnitude eliminating the potential Achilles heel of SSD-based storage systems.