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    Shedding some light on Intel X 25-V SSD benchmarking curiosities

    SSDelightful

      Hi All,

      Scott from Intel here. Before we get into the meat of this post, I wanted to let you all know that I’ll be doing a similarly technical  post once or twice a week either here, or on Intel technology blog here:

      http://blogs.intel.com/technology/

      (that’s me on the top!)

      If you guys want to get updates on when I’ve made a new post, follow the Intel SSD twitter account or become a friend on facebook. I’ll try to keep these portals free of junk and just give you guys access to the content. The Twitter account can be found here:

      http://twitter.com/intelssd

      and the facebook page can be found here:

      http://www.facebook.com/pages/Intel-Solid-State-Drive-Official/97164766102

       

      Let me know if you have any questions about Intel SSD social media. Anyways. The post.

       

      There have been a solid handful of questions regarding a strange occurrence that takes place while benchmarking read performance across the entire drive capacity of Intel’s X 25-V SSD. The drive is specified to achieve 170 MB/s sequential read speeds, but tests show the drive achieving read speeds above 200 MB/s, as seen in the graph below:

      pv_40gb_hdtune_read_not_full.png

      “Holy Cow!” - You

       

      How does it do that?  Well, as it turns out, the drive’s controller is doing something special. The controller has to keep track of where data is actually written in the NAND to be able to grab that data upon request from the host. As such, it also has to know where data is not written. Because accessing NAND takes some time (even if “some time” means “a ridiculously small amount of time”), the controller wants to make those NAND accesses as infrequent as possible.  And that’s where the secret sauce comes in; If the controller knows that a read request is being made for an area of NAND that has no data, it doesn't read the NAND, but instead reports back zeros. Therefore, the only time spent is the time the controller takes to process the SATA request.  This ends up yielding a very fast response rate and speeds in the neighborhood of 250MB/s.  So what you'll see, depending on how you have partitioned and written data to your SSD, is an area that performs in the neighborhood of 170MB/s (the area where data actually is) and an area that performs above 200MB/s. Keep in mind that some benchmark tests actually write data before reading.  If this is the case, you won't see any difference.  So, the take-away is this: be aware of the state of your SSD before hastily interpreting benchmarks.  If it is newer, with little data on it, then you'll see an unusually high sequential read performance.  If you’ve been using the drive for some time and have a fairly beefy chunk of data on it, then you'll get sequential read speeds that reflect the actual amount of time it takes to read from NAND.

       

      Same drive almost completely filled:

      pv_40gb_hdtune_read_full.png

      Drive with most data cleaned again:(Back to the same state as original.)

      pv_40gb_hdtune_read_not_full_2.png

       

      Feel free to post any questions/comments! I’ll do my best to answer!

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