840 EVO Read/Write Numbers

Discussion in 'MacBook Pro' started by endlightend, Nov 24, 2013.

  1. endlightend macrumors member

    Joined:
    Nov 5, 2013
    #1
    Can't find a better place to post than here- just installed a 250 GB 840 EV in my late 2011 MBP. I'm getting these numbers:
    [​IMG]

    Doesn't seem to match up with what's advertised on the website? But to be fair I'm also not sure what I'm supposed to be looking for. Anyone with their own EVO can confirm that this is accurate? System Report shows 6Gb/s and 6Gb/s negotiated.
     
  2. costica1234 macrumors member

    Joined:
    May 21, 2013
    Location:
    London
    #2
    I also have an EVO, however I got the 750 GB version and installed it on my 15 inch mid-2012 non-Retina MBP. Last month when I ran the disk speed test I got reads and writes of about 500 MB/s, just as expected.

    I suspect in your case it is lower capacity of the SSD which causes the writes to be slower. From what I know, the EVO uses a small part of the TLC as a SLC write buffer (which for the 250 GB version is just 3 GB) and thus the drive attempts to write at full speed to the buffer and when this becomes full it just transfers data to the slower TLC. Also, when running the Disk Speed Test you have to bear in mind that it does write a lot of GBs to the drive (in my case I noticed that it filled ~4-5 GB from my SSD when running it for like 10 seconds) and it may be the case that you ended up with the buffer full and the SSD was then transferring data directly to the slower TLC flash, thus the lower speed you got.
     

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  3. whitedragon101 macrumors 6502a

    Joined:
    Sep 11, 2008
    #3
    I have a 750 evo too in an early 2011 17" MBP

    Its gets

    Blackmagic :

    488MB/s Write

    512MB/s Read
     
  4. endlightend thread starter macrumors member

    Joined:
    Nov 5, 2013
    #4
    Thanks for the replies. On a couple review sites it mentioned the speed difference between lower and higher capacity versions of the EVO, but it seemed to be only by a few Mb/s instead of half the speed on the 250GB. Any other ideas? I'm going to fiddle with my trim settings and see if that did anything.
     
  5. endlightend thread starter macrumors member

    Joined:
    Nov 5, 2013
    #5
    Another update, the first time I click Start in BlackMagic, as it measures the write speed I'm getting results like this
    [​IMG]

    Then it measures the read speed, and after the test resets itself and measures the write speed again, I'm getting a drop to
    [​IMG]

    So am I only looking at the first measurement? Is it a matter of what costica mentioned that the first measurement is writing to SLC and then the second one goes to TLC, so my read/write numbers are actually fine?
     
  6. wwohl macrumors regular

    Joined:
    May 2, 2013
    #6
    OP,

    The EVO drives gain a lot of speed with the use of an internal cache. For the 250gb model, that cache is 3gb. File writes under 3GB will be fast but once the cache is exhausted, the read/write speeds will plummet to the original 840 series speeds

    You likely have the disk speed app set to 3GB or greater. Change the test size to 1GB and see what happens. Regardless, you're likely going to be seeing the 500/400 speeds during normal use. The app is just using a very large transfer size as its testing stimuli

    The cache allows them to have stellar performance for the average user and keep the price down. If you're a power user that is frequently writing large files, the 840 Pro series will provide more consistent high end performance.
     
  7. paul-n macrumors regular

    Joined:
    Jul 12, 2012
    #7
    The Evo provides maximum performance with 500 GB and higher capacities. read speed is always ~500 MB/s, but write speeds will decrease to 250 MB/s for the 250 GB model. For most customers this shouldn't be a problem because usually the source for such high rates isn't available.
     
  8. endlightend thread starter macrumors member

    Joined:
    Nov 5, 2013
    #8
    Exactly what I was looking for- thanks a bunch.
     

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