6 SSD Myths Debunked

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

Facts:

• 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

Facts:

• 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

Facts:

• 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

Facts:

• 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

Facts:

• 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

Facts:

• 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)