Mac Pro 3,1, PCIe SSD operating at only 2.5GT/sec

Discussion in 'Mac Pro' started by decryption, Apr 12, 2016.

  1. decryption macrumors newbie

    decryption

    Joined:
    Aug 2, 2006
    Location:
    Melbourne, Australia
    #1
    I picked up a Mac Pro 3,1 pretty cheap and chucked in a Samsung SM951 PCIe SSD, sitting in a Lycom DT-120 M.2 PCIe SSD to PCIe 3.0 x4 adapter (both purchased from RamCity, heh). It works well and boots fine, but the transfer speed is limited to only around 700MB/sec.

    Looking in system profiler shows me that whilst it's got 4x PCIe lanes, it's only operating at 2.5GT/sec, which would explain why benchmarking the SSD using Blackmagic's app only results in a max of 700MB/sec.

    Screen Shot 2016-04-12 at 12.10.28 PM.png

    This leads me to believe it's in PCIe 1.0 mode for some reason. The Lycom DT-120 is supposed to be good at this, it supports PCI 3.0 and 2.0. Dunno why the Mac Pro 3,1 has decided to operate it in PCIe 1.0 mode. The SSD is in Slot 2 (next to the graphics card - which is operating happily in 16x 5GT/sec mode), which is supposed to have full 16x PCIe 2.0 speeds, regardless of what's plugged in to slot 1. Or am I wrong?

    The only thing I can think of trying it another adapter off eBay (this one), but is there something else I'm missing here?
     
  2. h9826790 macrumors 604

    h9826790

    Joined:
    Apr 3, 2014
    Location:
    Hong Kong
    #2
    This adaptor doesn't like x16 slot, try to put it on another slot and check the system info again.
     
  3. 666sheep, Apr 12, 2016
    Last edited: Apr 12, 2016

    666sheep macrumors 68040

    666sheep

    Joined:
    Dec 7, 2009
    Location:
    Poland
    #3
    In other than x16 it will work @2.5GT/s for sure. PCIe 1,1 can't do more :D
    OP: SM951 seems to don't like the 3,1 (another MR member had this exact issue with it). XP941 should work OK. It's tied to SM951 being PCIe 3.0 while XP941 is 2.0 and it negotiates the link properly with 3,1.
     
  4. h9826790 macrumors 604

    h9826790

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    Apr 3, 2014
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  5. decryption thread starter macrumors newbie

    decryption

    Joined:
    Aug 2, 2006
    Location:
    Melbourne, Australia
    #5
    That's right - I put it in the other slots just to see and there was no change.

    Damn, that sucks :(
    Wonder if it'll work ok in a Mac Pro 4,1?
     
  6. Baunkjaer macrumors 6502

    Baunkjaer

    Joined:
    Feb 20, 2009
    Location:
    Copenhagen, Denmark
    #6
    Damn, that sucks :(
    Wonder if it'll work ok in a Mac Pro 4,1?[/QUOTE]
    It works fine in the 5,1
     
  7. vicentk macrumors regular

    vicentk

    Joined:
    Feb 24, 2008
    Location:
    Hong Kong
    #7
    you can try to put the PCie in slot 2
     

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  8. 666sheep macrumors 68040

    666sheep

    Joined:
    Dec 7, 2009
    Location:
    Poland
    #8
    If you'd click on his screenshot, you'd see the OP already has his SSD in Slot 2.
    Your Plextor SSD is PCIe 2.0 x2 and does not have the same issue with 3,1 as PCIe 3.0 SM951 has.
     
  9. isisism, Jul 30, 2016
    Last edited: Aug 3, 2016
  10. Theoprofil macrumors member

    Theoprofil

    Joined:
    Sep 23, 2016
    Location:
    Greece
    #10
    It works perfect on a mac pro 4.1 at slot number 3. Tested 100℅
    --- Post Merged, Nov 11, 2016 ---
    XP 941 works perfect at 3.1 with 5.0Gt speed . Tested100℅ by me. Sm 951 works as 2.5gt again tested 100℅ by me.
     
  11. sevichenko macrumors regular

    Joined:
    Oct 9, 2016
    #11
    thanks for the advice, i'm looking for a pcie ssd for my 3,1 MP
     
  12. Dan DC macrumors newbie

    Joined:
    Mar 6, 2017
    #12
    Me too - what did you find?
     

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