The dismal science of flash

The dismal science of flash

Summary: Economics isn't the only dismal science: the future of flash is even more dire than anything Malthus forecast. A paper presented at this week's FAST '12 conference, quantifies flash's declining reliability, endurance, and performance as density increases.

SHARE:

Researchers Laura M. Grupp and Steven Swanson from the UCSD Non-volatile Systems Lab and John D. Davis of Microsoft Research collected data from 45 flash chips from 6 manufacturers. Using that empirical data they predict the performance and cost characteristics of future SSDs.

It's not pretty.

Faster better cheaper or slower worse cheaper? While NAND flash is produced with semiconductor processes, it doesn't follow the normal virtuous circle of smaller feature size, faster performance, greater reliability and lower cost that we associate with the last 50 years of chip technology.

Why?

NAND flash traps electrons in quantum wells. As feature sizes shrink, so do the quantum wells and, more critically, the number of trapped electrons that store the information. That makes it harder to preserve and read the stored information.

Figures of merit While density, capacity and cost per bit improves with smaller feature sizes, the research found that every other figure of merit - performance, program/erase endurance, energy efficiency, and data retention time - all got worse as feature sizes shrink.

Based on past performance, the team derived equations to describe how changes in feature size have impacted key specs. They looked at SLC, MLC and TLC and feature sizes scaled from 72 nm to 6.5 nm (the consensus smallest feature size published in the International Technology Roadmap for Semiconductors (ITRS0), and assume a fixed silicon budget for flash storage.

Key results include

  • Latency. MLC write latency will double over time. Triple-level cell writes will grow to over 2.5MS, noticably reducing its performance advantage over disk writes.
  • Bandwidth. Small - 512B - read bandwidth and all writes decline by up to 50% over time. The impact is greatest on high-performance SLC flash.
  • IOPS. MLC flash I/O rates will drop almost in half.

Taken together the research suggests that flash may be not much better than disk in a few short years.

The Storage Bits take One important qualifier is that for the purposes of their modeling the team constrained the number of chips in the hypothetical future devices whose performance they predicted. While fine for isolating the impact of future chip shrinks, it ignores the potential of much greater parallelism for managing these changes.

Bandwidth drops by half? Double the number of chips.

But if something can't go on forever, it won't. NAND flash will soon enter an end-of-life crisis for computer applications that need performance. That's why ReRAM (resistance RAM) looks to be a good bet for replacing computer flash - not mobile device flash - over the next decade.

Comments welcome, of course. Here's a link to The Bleak Future of NAND Flash Memory (pdf).

Topics: Hardware, CXO, Networking, Processors, IT Employment

Kick off your day with ZDNet's daily email newsletter. It's the freshest tech news and opinion, served hot. Get it.

Talkback

8 comments
Log in or register to join the discussion
  • Betting man

    What's the over/under on how long it takes before some bozo wanders in and posts a comment about Adobe Flash?
    Robert Hahn
    • RE: The dismal science of flash

      @Robert Hahn
      Actually i would like to see that happen, Just to see if people actually read the articles instead of ranting or trolling..
      Anthony E
      • RE: The dismal science of flash

        @Anthony E I actually read the article and found out is was about flash memory rather than Adobe Flash which I expected, since it is dying even more quickly. Interesting article though. Storage Bits should have given it away.
        hayneiii@...
  • RE: The dismal science of flash

    I though Adobe was giving up on flash?

    Oh, silly me, guess I should have read the article :)
    gribittmep
    • RE: The dismal science of flash

      @gribittmep

      Ditto
      ScorpioBlack
  • I am thinking ASSRAM will be the next technology breakthrough.

    NT
    goingbust
  • RE: The dismal science of flash

    I could have sworn I heard of this well over a year ago. I thought I read something about NAND and nm size in some storagemojo comments, but I can't find them now. This research may have backed up the theory, but it's nothing new.
    eightmileshigh
    • RE: The dismal science of flash

      @doug.pirie@...
      You're correct about the knowledge of flash's limitations being well known in the industry. What is different about this paper is that they quantified what further feature shrinks will do to flash performance and longevity over the next 10 years.
      R Harris