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

  • PWL_Steve - Friday, September 23, 2011 - link

    I'm planning on buying an MBA soon so really appreciated the review of the display. For just about the same price, I could purchase the smaller iMac. Would it work the same way with a MBA as the Thunderbolt display would? Buying the IMac would allow my wife to have her own system and I would still be able to occasionally use it as a large display.
  • JasperJanssen - Saturday, September 24, 2011 - link

    No, the iMac in target display mode *only* provides a display. No power, no USB, no camera, and definitely no ethernet/firewire. I'm not sure about audio -- displayport Target Display Mode included audio as well as video, but the thunderbolt iMac is different enough that I don't know about that one.

    But as long as the display is all you want, sure, that works. Do keep in mind of course that the smaller iMac is a much smaller (cheaper) display.
  • tanjo - Friday, September 23, 2011 - link

    Apple, the biggest advocate of (almost)everything-in-one. Is it hard to separate the Thunderbolt to the display? If you find the Thunderbolt lacking and need to upgrade, you have to replace the Thunderbolt Display instead of just the Thunderbolt controller - a waste of a perfectly good display. How about making the Thunderbolt "box" dock at the back of the display? It'd still look clean. Reply
  • mcnabney - Friday, September 23, 2011 - link

    Like maybe a VESA-compliant box that attaches to the back of any monitor?

    The lack of logic astounds me.

    Oh, no, the iPeople couldn't handle the ugliness of a sleek box attaching to the BACK of their sleek display.

    /aren't we in a recession?
  • slashbinslashbash - Friday, September 23, 2011 - link

    No, there's no need to replace the Thunderbolt Display if something better comes out in the future. The beauty of Thunderbolt is that it is chainable, and the Thunderbolt Display has a chainable Thunderbolt jack. You can add an extra box in between the laptop and the Thunderbolt Display, or you can add an extra box after the Thunderbolt Display.

    Need USB3? I'm sure somebody will come out with a little box with a USB3 controller inside and a Thunderbolt interface. Your use of the Thunderbolt Display does not preclude your additional use of such a USB3 device: just plug it in to the Thunderbolt Display. Need an external GPU? Hook up the MBA to the external GPU Thunderbolt box, and then hook up that box to the Thunderbolt Display. Voila.

    You still get 100% use of the stuff built in to the Thunderbolt Display (USB2, GigE, FW800) and you get the additional use of whatever you tack on to the Thunderbolt chain, either before or after the display.
  • JasperJanssen - Saturday, September 24, 2011 - link

    There's not going to be an external GPU that can handle thunderbolt output any time soon. Mini Displayport, yes. Thunderbolt, no. And that means that it'll be a while before you can hook this particular display to an external GPU box, if ever.

    Everything except external GPU, yes, sure, that's what Thunderbolt is for and will combine great with this display. External GPU: for the time being, will require a VGA/DVI/DP display.
  • JasperJanssen - Saturday, September 24, 2011 - link

    Oh, and I forgot (but there's still no blasted edit button...): Your MagSafe cable will be in the wrong place, if you put a dock between the display and the laptop.

    Extension cables are available build-to-order at $199 according to google (seems to be they take a complete adapter, and graft a MagSafe laptop port onto it) -- easier just to get a second $99 adapter.
  • RandomUsername3245 - Friday, September 23, 2011 - link

    Since I decided to try using a Mac laptop for work about 6 months ago, and also observing others with Mac laptops, it seems like everyone has a rat's nest of wires running from every port on the computer to various peripherals. I think the lack of a docking station is a big negative for using a Mac laptop in a work environment. This new monitor almost fixes the problem, but unfortunately requires another "Apple Tax" payment. Reply
  • michal1980 - Friday, September 23, 2011 - link

    apple obsoletes ports, forces users to buy new products and its called...

    'Clean Brake'

    Microsoft doing something like that and there would be pitch forks.
  • Phynaz - Friday, September 23, 2011 - link

    What computers does Microsoft make? Reply

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