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6 SSD Myths Debunked

  • (Image: stuartmiles99)

  • Myth No. 1: SSDs wear out, don't have enough life for hard usage


    • Flash has a limited number of writes before data may not be stored properly
    • This is well-characterized
    • Solutions are:
         - Add spare space (over-provision) to the drive of 20+%
         - Build-in RAID-like error correction
         - Optimize use patterns; wear-leveling
         - Throttle writing to prevent hotspots
    • Result: Effective wear life differs between drive models, mainly on over-provisioning levels
    • Drive is specified as having either eight years of life at "NNN" terabytes or "N" full drive writes per day
    • Most use cases fit the lowest levels of data per day
    • Only a few cases need the most durable drives
    • Drives are often sold with two or more durability levels (good, better, best).

    Conclusion: BUSTED. Wear-out is no longer a concern.

    (Image: Imgorthand)

  • Myth No. 2: When powered down, SSDs lose data quickly


    • Heat DOES cause trapped electrons to tunnel faster, raising data-loss concerns
    • Theoretically, writing at low temperature and then storing at elevated temperature can cause data loss:
         - Models indicate write at 60 degrees F and store at 120 degrees F
    • This isn't realistic, though:
         - Typically, we write at 110 degrees F or higher, due to heat in servers
         - We store at room temperature, or well below if we use salt mines
    • This makes the self-erase problem not an issue
    • Moreover, the archive model has shifted
         - Users want faster access to their archived data (e.g. Facebook pics)
         - We use archives that are always plugged in
    • We've not had complaints of retention loss.

    Conclusion: BUSTED.

    (Image: xiaoke ma)

  • Myth No. 3: Hard drives have many more years of firmware development, making them better


    • This WAS true in the early days of SSDs
    • After nine years of development, today there is no gap
    • Still, SSD code continues evolving as hardware improves
    • Failure lifecycle is better understood
         - Error correction is improving
         - Effects of write patterns for small random writes are being addressed
    • So, the code is strong, but still evolving.

    Conclusion: BUSTED.

    (Image: Vermette)

  • Myth No. 4: Data reliability goes down with each die shrink


    • Smaller features on die mean fewer electrons stored in each cell
    • Each die shrink "node" reduces write wear life and data reliability
    • This requires software and sophisticated signal processing to overcome
    • Fear that NAND was hitting a wall and could not shrink further
    • 3D NAND resolves this:
         - Uses an earlier processing node; bigger features
         - Better wear-out
         - Better retention
    • Future capacity expansion is in 3D dimension; 64x and even 128x planned
    • Holds off the day when an alternative to NAND is needed

    Conclusion: BUSTED -- but it was close!

    (Image: donskarpo)

  • Myth No. 5: SAS isn't needed


    • SAS interfaces offer a little better performance over SATA (most SSDs use SATA interfaces)
    • SSD specs less dependent on SAS or SATA interface protocol than HDD
    • PCIe -NVMe is taking over super-fast drive market
    • SATA and NVMe are combining into SATA-Express
         - One interface solution for both top-end and bulk-tier drives
    • SAS is getting squeezed out
         - Let's simplify life and "go with the flow"!

    Conclusion: SAS ISN'T needed -- this really isn't a myth!

    (Image: Danil Melekhin)

  • Myth No. 6: SSDs cost more than hard disk drives


    • PCIe SSDs cost $2,000+ per terabyte; SATA SSDs from $300 and up
    • Enterprise SAS HDDs drives are $600+ and bulk SATA HDDs $35 per terabyte
    • 2 PCIe SSDs outperform a $200,000 HDD array
    • SATA SSDs outperform enterprise HDD by a large factor and are half the price
    • Bulk HDDs still beat SSDs on price
    • 3D NAND increases capacity per die by a big factor (64x layers in 2016, 8x capacity in 2017)
    • Fab processing increases by a much lower factor
    • Industry can back off two production "nodes"
         - Older fabs can be used, increasing production and yield while saving investment
    • Flash vendors predict price parity with bulk hard drives in 2017

    Conclusion: Myth partially busted already and fully busted in 2017.

    (Image: miki1991)

  • SSDs: The Realities

    • SSD is now mainstream
    • Performance is stellar
         - Random IOPS to 700,000 (versus 300 max for HDD)
         - Sequential transfers to 3+GB per second (HDDs achieve 150 MB per second)
    • SSD is low power, perhaps 1-2 watts compared with 12 W for HDD, though very high-end SSDs reach 10 W
    • No shock or vibration problems
    • Most SSDs use SATA interfaces
         - SAS is being replaced by PCIe- NVMe
         - SATA and NVMe are converging as a "SATA-Express" interface that can drive either protocol
    • Most drives have specified maximum write rates that guarantee eight years of life
    • SSDs are cheaper than enterprise HDDs
    • SSDs will soon be larger and cheaper than bulk SATA HDDs
    • With smaller capacities than an HDD can achieve, SSDs are cheaper in the embedded market.

    (Image: YuriyVlasenko)