Mac Pro Thunderbolt Bus Question

Discussion in 'Mac Pro' started by mBox, Sep 25, 2014.

  1. mBox macrumors 68020

    Jun 26, 2002
    Does anyone know how to do the math as far as bus consumption with the new Mac Pros?
    I have two Apple Cinema 30s, two Sonnet Echo Express III Rack with RED ROCKET in one and Pro Tools HDX PCI on the other, a G-Tech StudioRAID 8TB and a Black Magic Design UltraStudio 4K Video Converter.

    Ive tried numerous bus configs but it seems like the roll of a dice at times when running config with software such as Avid Media Composer, Pro Tools and Resolve.

    It fails at different levels and dont want to explain but if anyone can direct me to where one can find out of were sucking the life out of this thing.
  2. 65535 macrumors member

    Jul 20, 2011
    The math isn't too complicated, each of the 3 buses can push 20Gb/s so balanced your load on the 3 busses such that you stay under that 20Gb/s.

    I know for a fact that the raw data stream for dual 1440p 60Hz monitors (I have two of the Thunderbolt Displays) is right around 14Gb/s upstream. Throw a 2 disk RAID 0 enclosure on that same port and you start getting dropout on the second monitor as well as decreased write speeds.

    There is a concurrent I/O limit so be mindful.
  3. deconstruct60 macrumors 604

    Mar 10, 2009
    The bus consumption is more so that of the devices than of the Mac Pro.
    Which direction the devices are pushing/pulling data is critical to map out.

    The following note is on display configuration but implicitly usage of the ports for directly connected DisplayPort (or HDMI) helps map out Thunderbolt bandwidth availability.

    The suggestion there to spread the displays over multiple buses is to preserve TB bandwidth as much as anything to do with the displays themselves.
  4. deconstruct60 macrumors 604

    Mar 10, 2009
    Pragmatically, in this likely specific context ( directly connect the two legacy displays ) the 20Gb/s isn't the max working with. Mixed video data and PCIe transport will max out at 20Gb/s. PCIe all by itself isn't.

    Going to have about x3 PCIe v2 worth of bandwidth.

    Unless there is some sort of remote distance from Mac Pro requirement, putting the display's video data traffic onto any of the three TB buses probably isn't a good idea. There are more than a few devices here that need high bandwidth, low latency connectivity.

    Not just concurrency but also direction. Data capture (inbound relative to the Mac Pro ) and stream to storage (outbound) can go concurrently relatively unharmed because they are going in different directions. Multiple high bandwidth captures on the same bus concurrently would be a bad.
  5. mBox thread starter macrumors 68020

    Jun 26, 2002
    Thanks again for your wisdom :)

    Now when you say long distance and dont place onto any three busses, what the heck is my option on a new Mac Pro?

    Were using two Apple Cinema 30"s with a Gefen Dual-Link DVI Switcher at about 10 foot extension using DVI.

    So you dont suggest putting both on one bus but split and share with other peripherals.

    can you be specific as to what is safe out of the listed options I have below:

    Sonnet Echo Express III Rack - RED ROCKET PCI Card
    Sonnet Echo Express III Rack - Digidesign HDX PCI Card
    Black Magic UltraStudio 4K
    GRAID Studio 8TB

    I have had a chance to go through their specs so please bare with me.
  6. deconstruct60 macrumors 604

    Mar 10, 2009
    There is a difference between what Apple labels the TB bus and pragmatically real bus. A DisplayPort device directly hooked to Mac Pro's Thunderbolt port is pragmatically not on the Thunderbolt bus. It is in legacy "pass thru" mode. That signal is not being encoded into TB data traffic and transported on a TB network("bus").

    Long distances comes not directly connecting the Display to the Mac Pro. Either connecting them to a "downstream" TB device and plugged in there. Either can extend a few meters with normal TB copper cable or much father with TB fiber but both put video traffic onto the TB newtork/bus.

    a mDP DVI dongle to 10 foot DVI cable is still pragmatically a direct connection to the Mac Pro. There is no TB network involved in that chain. As long as follow the wire(s) back to the Mac Pro and don't cross any TB devices then it isn't a TB network.

    That would be extremely dubious. Each of the three TB controllers is connected to two physical ports. If you connect two devices in legacy DisplayPort mode to those to ports, then pragmatically what you have down is flushed the PCIe connection of that controller down the drain.

    With twice a many devices that need PCIe data transport than DisplayPort/Video data transport that is even more short sided. Fit the higher number devices with enough bandwidth and then use the left over ports for the smaller number of legacy data transport.

    If primarily using the RED ROCKET card to read from bulk storage and transcode back to the same bulk storage then I would separate those two onto independent buses. Those are two good candidates for the legacy DP/DVI video traffic. Since RED Rocket is really looking for at x8 PCIe link it should be on the TB bus by itself. So one legacy monitor on that other port.

    If Blackmagic UltraStudio is being used equally for capture and display ( often have bidirectional traffic) then placement is a bit more of judgement call. If not used concurrently with the ROCKET card much then maybe able to share. If it is then pragmatically don't have much of a choice as have three higher bandwidth,bidirectional players and three TB buses.
  7. mBox thread starter macrumors 68020

    Jun 26, 2002

    Thanks again deconstruct60 for the tips.

    So far I havent had issues with the following Thunderbolt config:

    Thunderbolt Bus 1
    Port 1 - Apple Cinema 30"

    Thunderbolt Bus 2
    Port 2 - Black Magic Design UltraStudio 4K

    Thunderbolt Bus 0
    Port 5 - Apple Cinema 30"
    Port 6 - GRAID STUDIO 8TB

    Where the issues start is when Pro Tools start to hiccup switching back and forth with Avid Media Composer.
    Not once did I see an issue with the RED ROCKET which is usually the first culprit in these kind of setups.
    The card is someone useless due the shear speed of the new Mac Pro but there are days when I want to see 4K/5K clips at FULL DEBAYER plus it does help speed up transcoding from R3D to <insert format here>

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