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How We Test HDDs And SSDs

Final Thoughts

Several exciting changes will affect the client storage market this year. SSDs are on track to receive a higher-performance interface and simplified set of commands. At the same time, flash is growing up (literally). These advancements will divide the market. While lower-cost products rival mechanical storage on the value front, high-performance products will allow new applications to thrive. 

The two buzzwords for 2015 are Non-Volatile Memory Express (NVMe) and 256-bit 3D NAND. NVMe is a set of commands that unbinds NAND from the limitations of the Advanced Host Controller Interface. AHCI was introduced as the register-level interface for SATA. When SATA was introduced, flash in the densities we have today wasn't on the horizon. Back then, hard drives were going to rule for decades. Of course, their mechanical nature capped performance, limiting the utility of deep queue depths. SATA capped native command queuing at 32 queues of one command (far more than was needed). NVMe increases this limit to 64,000 queues, and each queue can sustain up to 64,000 commands.

NAND flash is advancing, too. Improvements in manufacturing technology already enabled the first 3D V-NAND from Samsung. IMFT will follow with 3D flash by mid-2015, and it's rumored that we'll see 256Gb densities. Overnight, 1TB SSDs will turn into 2TB SSDs. The manufacturing costs should be equal once the dust settles, so your wallet won't suffer when it comes time to step up capacity.

Also on the flash front, expect more three-bit-per-cell flash, also referred to as TLC. Many of the charts in this editorial show an unbranded SSD under the SMI SM2256 name. This is a R&D board from Silicon Motion with a new controller that should hit the market in a few months. It's designed to support cheap TLC flash with P/E cycles as low as 500. Advanced LDPC algorithms are expected to extend low-cost flash life to the levels we enjoy today. So, by the end of 2015, 256GB SSDs may sell for as little as $50.

The new high-performance products will definitely require some tweaking to our test methods. But the low-cost stuff probably will as well. Faster storage is expected to hit ceilings limited by its host interface, PCI Express. Currently, that means a four-lane PCIe 3.0 link, or 32Gb/s. PCIe 4.0 isn't too far off either. LDPC will adapt to changing flash as the medium wears. If an error occurs, the controller goes back to reread the flash cells. This will increase latency.

We are already seeing the effects of low-cost TLC flash causing issues with performance loss in Samsung's 840 EVO. That drive's 1xnm NAND shows signs of read retries after just a few months of data at rest. If Samsung shuffles the information too often, the product won't satisfy its minimum warranty standards. It's a tough position to be in for the best-selling consumer SSD of all time. In the coming months, we'll roll out a new test for the condition in question. And because this is a living document, we'll fill you in first.


MORE: Best SSDs For The Money
MORE: Storage in the Forums

Chris Ramseyer is a Contributing Editor at Tom's Hardware, covering Storage. Follow him on Twitter @chrisramseyer and on Facebook. Follow us @tomshardware, on Facebook and on Google+.

  • damric
    How I test an SSD. HARD RESET my computer 20 times. If the SSD is still recognized by the motherboard, then the SSD controller is worth a flip.

    SSDs will never wear out due to IOPs. Only the controllers break. Quit kidding yourselves.
    Reply
  • schizz69
    Great article. Always good to get a glimpse inside the process, which Tom's is always so willing to do.
    Thanks Chris.
    Reply
  • ssdpro
    You'll notice all these review sites keep their tests nice and short. That way Samsung stays happy and keeps buying ad space. If they tested a drive months apart Samsung would be exposed with those floppy disk slow reads.
    Reply
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  • Gurg
    None of these tests give the consumer any indication of the degredation of the performance of the SSD over time. While my systems have been become more powerful and the software has been updated, the performance of my main SSD used mostly for for W7 and hardware drivers and as measured by Passmark runs has declined by 38% in about three years.
    Reply
  • unityole
    @Gurg, as SSD over time, either via temperature or usage or amount of data filled performance declines. if you secure erase and install new window and it'll back to brand new performance again, tbh i think this article cover most of it, maybe you're just confused between a good ssd or uncleaned window files slowing down your system.
    Reply
  • ykki
    How I test an SSD. HARD RESET my computer 20 times. If the SSD is still recognized by the motherboard, then the SSD controller is worth a flip.

    And that will be all on your first day of "How to test hardware the MacGyver way"

    Tomorrow we will learn to test psu's by putting them in microwave at 50 degree C for 60 minutes while it itself is powering the microwave.
    Thank you. :lol:

    Reply
  • damric
    15491425 said:
    How I test an SSD. HARD RESET my computer 20 times. If the SSD is still recognized by the motherboard, then the SSD controller is worth a flip.

    And that will be all on your first day of "How to test hardware the MacGyver way"

    Tomorrow we will learn to test psu's by putting them in microwave at 50 degree C for 60 minutes while it is powering the microwave.
    Thank you. :lol:

    I choked on my drink you had me LOLing so hard :)
    Reply
  • unityole
    15491425 said:
    How I test an SSD. HARD RESET my computer 20 times. If the SSD is still recognized by the motherboard, then the SSD controller is worth a flip.

    And that will be all on your first day of "How to test hardware the MacGyver way"

    Tomorrow we will learn to test psu's by putting them in microwave at 50 degree C for 60 minutes while it itself is powering the microwave.
    Thank you. :lol:

    calm down!!
    Reply