Thunderbolt Performance

The Eagle Ridge Thunderbolt controller is home to two Thunderbolt channels, each one is good for up to 10Gbps in either direction (up or downstream). That works out to be 20Gbps of bandwidth per channel or 40Gbps aggregate between the two. You can only send two channels worth of data down a single Thunderbolt cable, so there's no point to having more than two from a performance standpoint unless you have more than one port on your system.

If DisplayPort and PCIe traffic are indeed carried on separate channels, then the Thunderbolt Display by itself is eating up around 70% of the bandwidth of a single channel on its own (2560 x 1440 x 32bpp x 60Hz with 8b/10b encoding > 6.75Gbps). That leaves 10Gbps in each direction for PCIe traffic. If we look at our benchmarks from the previous section we see that we can hit just under 2Gbps with all of the auxiliary interfaces (GigE, FW800, USB2) running. Given our previous investigation with the Promise Pegasus we know that 8Gbps is feasible there as well. It's possible, that with everything running at once, we could actually run into bottlenecks with Thunderbolt.

To find out I ran a few tests. First I needed a baseline so I threw four SF-2281 SSDs into the Pegasus R6 chassis and configured them in a RAID-0 array. I ran a 2MB sequential read test (QD=16) and measured 909MB/s from the array. This value was obtained without the Thunderbolt Display connected, only the Pegasus R6.

Next I connected the Thunderbolt Display directly to my test MacBook Pro, and then connected the Pegasus to it. I repeated the test, this time getting 900MB/s. Thankfully the presence of the Thunderbolt Display doesn't seem to impact the max data rate I can get from the Pegasus.

For my third test I added a Gigabit Ethernet transfer from a file server to a local SSD using the GigE port on the display. During this test I was also playing back music using the Thunderbolt Display's internal audio codec and speakers. I re-ran the Pegasus test and got 855MB/s.

For my final test I re-ran the third test but added a FireWire 800 to USB 2.0 SSD transfer, both connected to the Thunderbolt Display. I also fired up the FaceTime HD camera on the display using Photo Booth and left it on during the test. The final performance score from the Pegasus was 817MB/s.

Apple Thunderbolt Display Performance

With everything running Thunderbolt performance took a 10% hit. Note that the standard Pegasus configuration isn't able to hit these data rates to begin with, so unless you've pulled out the 12TB of storage and stuck in your own SSDs you won't see any performance drop.

What this does tell me however is the ultra high end users that are looking to daisy chain multiple Thunderbolt storage boxes together may not want to do so. I only have a single Pegasus R6 on hand, but I'm guessing there will be significant performance drop off after the first box. Not that I'm complaining about being able to push nearly 1GB/s over a $49 cable from a notebook, I'm just trying to give a heads up to those who may have aspirations of even higher performance.

Testing the Pieces Display Testing - Color Quality & Uniformity


View All Comments

  • mczak - Friday, September 23, 2011 - link

    I'm wondering what the performance would be like? Looks to me like you'd get a far bigger performance hit in this case. Reply
  • Constructor - Friday, September 23, 2011 - link

    That would be very interesting indeed.

    In a discussion over at ars I've been speculating about some of the possible complications with that setup:
    (Same user name there.)

    Anand, it would be very interesting if you could find out more about the inner workings and the performance consequences of such a combination, possibly confirming or disproving my speculation on the matter.

    Over at Macworld they even seem to have made a Cinema display work when plugged in to a Pegasus RAID daisy-chained to a Thunderbolt display. The implications of that and the potential impact on Thunderbolt throughput would be most interesting as well... ;-)
  • AlexCheng - Friday, September 23, 2011 - link

    Sorry guys, but maybe I didn't quite catch it; what exactly is it using as its power supply source? Because it said that the MagSafe port could charge your MacBooks, then where the hell is the cable for its power?? Reply
  • Constructor - Friday, September 23, 2011 - link

    The display has an ordinary power cable which you'll need to plug into a wall outlet. And the display then powers and charges the MacBok Air/Pro. Reply
  • ltcommanderdata - Friday, September 23, 2011 - link

    If Apple goes through with removing the optical drive for the MacBook Pro, hopefully they'll add an optical drive to the Thunderbolt Display. That would make the Thunderbolt Display very complete as a dock. Reply
  • dBoze - Friday, September 23, 2011 - link


    When you mention there is "no analog audio out", I think the inclusion of even analog audio would be a bit of a slap in the face. All Macs in recent history include digital audio through the 1/8" jack via 1/8" TOSLINK, Us Mac users are far too cool for analog ;).

    Another solution for digital audio without an extra cable to your MacBook would be using AirPort Express. This will give you a digital or audio connection to your speakers over the network, and you can even plug it into your network via ethernet if your wireless signal isn't too strong. If I recall correctly, you can choose your AirPort Express as the "device for sound output" under the "Output" tab in "Sound" under sys preferences. Of course, you're limited to using AirPlay-compatible applications (iTunes) on the Windows side of things.
  • Constructor - Friday, September 23, 2011 - link

    All recent Macs have both analog (electrical) and digital (optical) audio ports in the same socket. Analog is for convenience, digital is for avoidance of ground loops and of analog signal degradation.

    An additional audio port (USB/FireWire/Thunderbolt) is possible, if inconvenient.
  • stanwood - Friday, September 23, 2011 - link

    Nice review!

    A lot of comments about how Apple could have built this display is a way that made it more easily upgradable. This is a PC mentality (which I share). Apple rejects it. Don't waste your time asking for it. If you must have some Mac love, use these 3 simple rules:

    1) Buy all your Apple gear in a single release cycle.
    1a) Go ahead and upgrade the OS. Those are actually pretty cheap.
    2) Use it until you hate it or can't resist getting the new shiny stuff.
    3) Give it all to your grandfather, aunt, or Goodwill and return to step 1.

    By the time you get to step 3 Apple will have replaced all the important I/Os. There will be no point in trying to upgrade.
  • mcnabney - Friday, September 23, 2011 - link

    Large, high quality displays are expensive, but last a long time. The iMac and displays like this compell people to discard those expensive displays far ahead of their time and likely buy another display of the same size and resolution.
    My 27" display is on its third computer and it provides better color accuracy than this expensive new one. That is probably my biggest beef with Apple, sending so many nice IPS displays into the trash/closet long before they wear out or become outdated.
  • slashbinslashbash - Friday, September 23, 2011 - link

    Not any more. Starting with the 2010 27" iMac, there was a DisplayPort which was both an input and an output. Now with all the 2011 iMacs having Thunderbolt, they can all be used as displays for other computers with Thunderbolt display output. Reply

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