Thursday, December 10, 2015

SSDs: Cheap as Chips?

Four and a half years ago Ian Adams, Ethan Miller and I proposed DAWN, a Durable Array of Wimpy Nodes, pointing out that a suitable system design could exploit the characteristics of solid-state storage to make system costs for archival storage competitive with hard disk despite greater media costs. Since then, the cost differential between flash and hard disks has decreased substantially. Below the fold, an update.

Lucas123 at Slashdot reports:
Hard disk drive per-gigabyte pricing has remained relatively stagnant over the past three years, and prices are expected to be completely flat over at least the next two, allowing SSDs to significantly close the cost gap, according to a new report. The report, from DRAMeXchange, stated that this marks the fourth straight quarter that the SSD price decline has exceeded 10%. ... However, through 2017, the per-gigabyte price of HDDs is expected to remain flat: 6 cents per gigabyte. Consumer SSDs were on average were selling for 99 cents a gigabyte in 2012. From 2013 to 2015, the price dropped from 68 cents to 39 cents per gig, meaning the average 1TB SSD sells for about $390 today. Next year, SSD prices will decline to 24 cents per gig and in 2017, they're expected to drop to 17 cents per gig.
In October, in a post based on Robert Fontana's excellent slides from the Library of Congress Storage Architecture workshop, I wrote
dividing the $/GB for flash by the $/GB for hard disk gives us the cost ratio and the following table:

  • Year  Cost Ratio
  • 2008 12.2
  • 2009 13.1
  • 2010 17.7
  • 2011 11.6
  • 2012 7.8
  • 2013 8.7
  • 2014 8.4
Adding the projections from the DRAMeXchange report gives us:
  • 2015 6.5
  • 2016 4
  • 2017 2.8
Based on Fontana's work, discussions at the Storage Valley Supper Club, and the track record of industry analyst projections, I'm skeptical of these projections, for two reasons:
  • Flash is inherently a more valuable medium than hard disk, so will command a price premium even if manufacturing costs per GB were equivalent.
  • Flash supply is constrained by fab capacity, which is inadequate to displace much of the hard disk volume.
Nevertheless, a change from solid state media being more than an order of magnitude more expensive to being perhaps a factor of three more expensive would greatly strengthen the case for DAWN. Although there are increasing signs that the storage industry is thinking along these lines, it will clearly be some time before our analysis bears fruit.

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