USB 3 Slower on nMP

Discussion in 'Mac Pro' started by Eziggy, Jan 7, 2014.

  1. Eziggy macrumors newbie

    Joined:
    Sep 7, 2010
    #1
    Hi All,

    First time poster, long time MacRumors reader. A quick thanks to everyone here for their great insights over the years.

    I just received the nMP (6-core/16GB/512GB/D700) and started setting it up. I noticed something interesting - I tested the speed of my external USB 3.0 drive and noticed it ran at least 50-60MB/s slower than on my 13" rMBP (2013).

    The external drive is an Intel 520 480GB SSD in an Oyen Digital USB 3/eSATA enclosure. On the rMBP it works amazing, actually was faster than the Seagate thunderbolt adapter, which I sent back.

    AJA: ~400MB/s read/write on the rMP vs. mid-300s on the nMP
    BlackMagic: 400+ read on the rMBP, mid-300s on the nMP

    Anyone else noticed this or would know why this is?

    Thanks!
     
  2. Cubemmal macrumors 6502a

    Joined:
    Jun 13, 2013
    #2
    Yup, two things. The chipset still doesn't include USB 3, so that's on an external USB controller. Two, by the time you get to USB the system is running out of PCIe lanes. Check the Anandtech article, I forget how many the USB system gets but it's not a lot. Regardless he warns you not to use USB in the hopes of it being a poor mans Thunderbolt.

    If you have USB disks you want to use, you'd probably be better served by putting them on the Thunderbolt chain via a USB adapter or dock. USB3 on the nMP should only be light duty like keyboards and the like.
     
  3. motegi macrumors regular

    Joined:
    May 14, 2009
    Location:
    sydney.au
    #3
    USB adapter? I thought a dock was required to switch out the pin signals etc?
     
  4. paulrbeers macrumors 68040

    Joined:
    Dec 17, 2009
    #4
    As already stated, technically the USB bus only gets 1 PCIE 2.0 lane which only works out to 4 gb/s instead of 5. I wouldn't go as far as to say the USB 3.0 is only good for keyboards, but it will be slower for SSDs and RAIDs. Regular hard drives won't have any issues.
     
  5. Anim macrumors 6502a

    Anim

    Joined:
    Dec 16, 2011
    Location:
    Macclesfield, UK
    #5
    Doesn't USB3 share lanes with one of the TB controllers? If your using a TB port for your monitor try it in a diff socket and see if that makes a difference? No idea if that idea has any merit just a wild suggestion.
     
  6. Cubemmal macrumors 6502a

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    Jun 13, 2013
    #6
    I just mean any TB device with USB ports on the other end, there are a variety of solutions.
     
  7. paulrbeers macrumors 68040

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    Dec 17, 2009
    #7
    Anandtech believes it has it's own PCIE lane BUT one PCIE 2.0 lane wouldn't supply enough bandwidth for full USB 3.0

    The TB ports are off of the CPUs PCIE 3.0 ports

    http://anandtech.com/show/7603/mac-pro-review-late-2013/8
     
  8. Eziggy thread starter macrumors newbie

    Joined:
    Sep 7, 2010
    #8
    Thanks! That makes sense, looks like Thunderbolt it is then. Bummer on the limited USB 3.0 throughput, looking forward to seeing more thunderbolt enclosures.

    ----------

    Thanks, it's unfortunate there aren't many decent Thunderbolt 1 or 2 enclosures. Looks like a dock is the way to go.
     
  9. Anim macrumors 6502a

    Anim

    Joined:
    Dec 16, 2011
    Location:
    Macclesfield, UK
    #9
    Ah yes, It was the HDMI port that shares with Thunderbolt

    [​IMG]
     
  10. bcuzawd macrumors member

    bcuzawd

    Joined:
    Dec 25, 2013
    #10
    Great info!

    USB 3.0 external drive has now officially been removed from my "is this a good alternative" list.
     
  11. beaker7 macrumors 6502a

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    Mar 16, 2009
    #11
    Each day we find new ways the nMP is throttled.
     
  12. Dranix macrumors 6502a

    Dranix

    Joined:
    Feb 26, 2011
    Location:
    Gelnhausen, Germany
    #12
    Each day we find another one to whine on it. If it doesn't fit your reqs get something different. This whining leeds to nothing.
     
  13. vmacrob macrumors newbie

    Joined:
    Jan 8, 2014
    #13
    I don't think this is correct. Anandtech states "A single PCIe 2.0 lane offers a maximum of 500MB/s of bandwidth in either direction (1GB/s aggregate), which is enough for the real world max transfer rates over USB 3.0"

    USB 3 is 5 Gbps bi-directional, PCIe 2.0 is 1 GBps (or 8 Gbps). So, there shouldn't be a limitation, at least when one device is used.
     
  14. Bear macrumors G3

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    Jul 23, 2002
    Location:
    Sol III - Terra
    #14
    Shouldn't you be comparing the single direction speed of PCIe to the speed of USB 3.0. The reason I suggets this is if you're doing mostly reads or mostly writes, it's the maximum single direction speed you need to compare.
     
  15. analog guy macrumors 6502

    Joined:
    Mar 6, 2009
    #15
    small tangent: has anyone seen a similar breakdown for the late-2013 iMacs?

    this information has been good as i plan my external storage strategy for my nMP, but i wonder if the iMac is similarly affected (i.e. if the storage strategy for an iMac would have the same considerations as one for the nMP).

    i suspect the iMac has more lanes open to it because lanes are not taken up by a 2nd graphics card.

    thanks!
     
  16. vmacrob macrumors newbie

    Joined:
    Jan 8, 2014
    #16
    Ah, you are correct. I was thinking that USB 3.0 was 2.5 Gbps each way - but it's 5 Gbps each way.
     
  17. paulrbeers macrumors 68040

    Joined:
    Dec 17, 2009
    #17
    IMac wouldn't be affected because the chipset actually has USB 3.0 built in. Because Xeon processors are server chips it has no native USB 3.0 and thus needs to "steal" the bandwidth from PCIE. Also there aren't multiple thunderbolt lanes in an iMac like there are on the Mac Pro.
     
  18. analog guy macrumors 6502

    Joined:
    Mar 6, 2009
    #18
    thank you. are the two TB ports on the iMac sharing bandwidth, then (similar to how members of each of the 3 pairs of ports on the nMP share a lane)?
     
  19. crjackson2134 macrumors 68020

    crjackson2134

    Joined:
    Mar 6, 2013
    Location:
    Charlotte, NC
    #19
    If you are going to use Platter drives, I would think the USB ports would work just fine (save fast Raid 0). I would rather invest in a good TB Dock that supports USB 3 if you need SSD or fast Raid on USB. If you're willing to spend this much on a nMP, then do it right.

    Honestly, unless really vested in USB 3.0 devices, I'd rather go with TB anyway.
     
  20. motegi macrumors regular

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    May 14, 2009
    Location:
    sydney.au
    #20
    If I'm running my RAID5 box of 7200rom disks over USB3, it's not really gonna matter right? Since the drive speed will be the bottleneck not the bus?
     
  21. d-m-a-x macrumors 6502

    Joined:
    Aug 13, 2011
    #21


    ----------

    It sounds like It will be fine so long as you use only one usb3 port, for all 4 ports only have one lane. Beyond that a dock may speed things up if configured right
     
  22. Derpage Suspended

    Joined:
    Mar 7, 2012
    #22
    Yes, yes. Let's embrace poorly executed design at it's best. This is either bad design, or it's a blatant attempt to push TB2.0. Either way, another iToy innovation at it's finest.
     
  23. motegi macrumors regular

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    May 14, 2009
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    sydney.au
  24. d-m-a-x macrumors 6502

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    Aug 13, 2011
    #24
    I had some interesting usb bus issues with the cMP as well -
     
  25. VirtualRain macrumors 603

    VirtualRain

    Joined:
    Aug 1, 2008
    Location:
    Vancouver, BC
    #25
    I'm actually surprised there's a storage solution that can push USB3 to the limit. Hat's off to Oyen Digital. For some strange reason, most USB3 enclosure tests I've seen can't come close to filling USB3's bandwidth. The only other enclosure that could push over 400MB/s is the FirmTek miniSwap that Barefeats tested a while ago.

    Personally, I don't care, since I don't have anything that can push USB3 beyond 400MB/s anyway, but if I play arm-chair nMP product manager for a moment... I think it would have been ideal if Apple had opted for two dual-port USB3 chipsets, each on a separate PCIe lane. As I understand it from Anand's article, the USB3 chipset got a single lane along with each GigE port and the Wifi. They could have muxed all the networking onto two lanes (or even a single lane without bottlenecking anything there) and that would have given them two lanes for the USB3. The way it is it's a bit of a lazy/cheap design decision.

    EDIT: BTW, almost every USB3 PCIe add-on card I've seen, is PCIe x1 also so this is hardly without precedent.
     

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