rMBP 15" - Two USB 3.0 ports, 2 different transfer speeds

Discussion in 'Mac Accessories' started by foto-max, Jun 27, 2013.

  1. foto-max macrumors newbie

    Joined:
    Oct 18, 2011
    #1
    My rMBP 15" is acting funny in that when attaching a Samsung 830 128GB SSD directly to the laptop's two USB 3.0 ports sequentially, I will randomly have transfer speeds of either under 50 GPS or over 200 GPS. Any thoughts?
     
  2. simsaladimbamba

    Joined:
    Nov 28, 2010
    Location:
    located
    #2
    How do you measure the transfer rate and can you tell us what kind of unit "GPS" is? Transfer rates are either measured in Bits per second (bps or b/s) or Bytes per second (Bps or B/s), thus you should report it in either xy Megabit/s (Mbps or Mb/s) or xy MegaByte per second (MBps or MB/s).
     
  3. waw74 macrumors 68030

    Joined:
    May 27, 2008
    #3
    get blackmagic disk speed test from the app store.

    it will give you the most consistant numbers, and provides a good benchmark when comparing multiple situations.
     
  4. foto-max thread starter macrumors newbie

    Joined:
    Oct 18, 2011
    #4
    Sorry, had a little too much caffeine this am. The speeds I quoted are of course Mbps and were obtained with Blackmagic.
     
  5. simsaladimbamba

    Joined:
    Nov 28, 2010
    Location:
    located
    #5
    If they were Mbps then it would be under 6.25 MB/s or over 25 MB/s. But I guess you experienced 50 MB/s and 200 MB/s.

    You could also try these:
     
  6. foto-max thread starter macrumors newbie

    Joined:
    Oct 18, 2011
    #6
    Nonetheless, any idea as to why there is this discrepancy between the two ports?
     
  7. simsaladimbamba

    Joined:
    Nov 28, 2010
    Location:
    located
    #7
    One port reports 50 MB/s and less, and port reports 200 MB/s and more?
    Maybe it has something to do with power?
     
  8. foto-max thread starter macrumors newbie

    Joined:
    Oct 18, 2011
    #8
    The laptop is continuously on ac power. It has been rebooted a number of times without effect. All OS and programs are currently up to date.
     
  9. lederermc macrumors regular

    lederermc

    Joined:
    Sep 30, 2014
    Location:
    Seattle
    #9
    My (old) understanding is that Unix uses otherwise free memory as file buffers. The first time you run a test a given file is read/written from/to actual disk. The seconds time it may be in central memory. As mention by waw74, black magic speed tester propably would not be affected by this.
     
  10. Gav2k macrumors G3

    Gav2k

    Joined:
    Jul 24, 2009
    #10
    One port is on the logic board the other is on a daughter board.

    I'm guessing your getting the faster connection on the MagSafe side?
     

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