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
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  • Ryan Smith - Friday, September 23, 2011 - link

    We replaced the video a couple of hours ago with one that has better audio. You shouldn't be seeing any links to the old one (and if you are, please say where). Reply
  • KPOM - Friday, September 23, 2011 - link

    Are there any technical reasons for using Eagle Ridge in the Thunderbolt Display instead of Light Ridge, or is it just Apple being Apple? Had they used the latter, it would have been possible to daisy chain a Cinema Display directly to the Thunderbolt Display, right?

    Also, on page 8, there is a slight error. You say "The MacBook Air is a different story. Not only does it only support two displays, but the Light Ridge controller only has a single DisplayPort input so you're not driving more than one external display via a MBA no matter what you do."

    I think you meant to say "Eagle Ridge" controller.
    Reply
  • -=Hulk=- - Friday, September 23, 2011 - link

    Why does Intel doesn't use the daisy chaining feature of DisplayPort 1.2 instead of encapsulating individual DP v1.1 streams??? Reply
  • Ryan Smith - Friday, September 23, 2011 - link

    If I had to go out on a limb, a single TB channel doesn't have enough bandwidth for DP 1.2. Reply
  • Trefugl - Friday, September 23, 2011 - link

    I really really love the features that thunderbolt adds to the MBAs (e.g. FireWire and GigE), but I don't want to have to upgrade my entire monitor every time I want to upgrade to the next hub (for maybe USB3 support, or more ports, etc). This would only get worse if they started to put GPUs into the monitor, as GPU tech becomes significantly outdated every year or two, whereas a good monitor can last you 5+ years. Why can't they just release a sleek HUB that you can have sitting behind your monitor. Their approach just doesn't make sense if you already have a 27" or 30" monitor (nor for future upgrades). Reply
  • slashbinslashbash - Friday, September 23, 2011 - link

    If you already have a 27" or 30" monitor, then yes, this doesn't make as much sense. If you are just now buying such a monitor, then the Thunderbolt Display makes perfect sense. There is nothing keeping you from buying a future box/hub that you describe, and using it between the MBA/MBP and the display (if the box/hub has a built-in GPU) or daisy-chaining it after the display (if you just want USB3 or other ports). That's the great thing about Thunderbolt, you can keep adding on to it. This display is not necessarily the final link in the chain, nor is it necessarily the first link in the chain. It provides useful functionality at a competitive price today, and the add-on capabilities of Thunderbolt will continue to be useful as new tech comes on line. Reply
  • Trefugl - Friday, September 23, 2011 - link

    But what happens when the "next cool thing" comes out that we want in our monitors? Do you just replace a perfectly good monitor because you want to upgrade the addons? I suppose my feelings towards this stem more from the iMac, where you trash a good monitor every few years because you want a new all in one PC... Reply
  • slashbinslashbash - Friday, September 23, 2011 - link

    Nobody trashes their old iMacs. The secondary market for Macs is huge. It's not like the PC world where your 3-year-old CPU and mobo would go for $100 so you just keep them as backup or put them into a machine for folding or something. With iMacs, if you upgrade at 3 years then you can probably still get around 40-50% of what you paid for it. 2008 iMacs are regularly going for $600+ on eBay. You buy a new one, transfer everything over, and sell the old one. It's almost like buying a car where you 'trade in' your old model. Reply
  • HMTK - Friday, September 23, 2011 - link

    This must be a US phenomenon then. Reply
  • jecs - Friday, September 23, 2011 - link

    Well, not a US exclusive or phenomenon.

    It happens worlwide because most Mac laptops or Pro Macs have been traditionally decent machines (not the best or the most specialized but sure not the cheapest). Some people like OSX but doesn't want to expend on new hardware.

    And not a phenomenon because this is not exclusive to Macs but to many decent products that age well including speakers, cars, movies or albums and many more things.
    Reply

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