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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  • mcturkey - Friday, September 23, 2011 - link

    I guess I really don't understand why they can't just make a non-integrated docking station. Use Thunderbolt to connect it if need be, but making it part of the display seems to just add a very unnecessary expense increase if you find yourself needing a new monitor or different/more/better ports in the future. Reply
  • Constructor - Friday, September 23, 2011 - link

    As far as I'm aware there are already multiple external PCIe slot housings and other adapters on the way which will effectively serve that purpose.

    And all of them will be usable with any Mac or PC which has suitable PCIe drivers for the respective ports, so Thunderbolt can indeed provide the long-missing "universal dock".

    The complication may be that these drivers should be able to survive hot plugging if you want to avoid having to reboot the machine every time you (dis)connect such an external box (or possibly risk a blue screen / kernel panic otherwise).

    Apple just chose to make one specific bundle product; They're leaving all the other possibilities to third parties so far. Once such alternatives are on the market, it's simply your choice.
  • SameerRamesh - Friday, September 23, 2011 - link

    My strong gut feeling suggests that apple will bring only USB 3.0 ports to all their next-gen Macs. Why?
    Intel's IVB chipsets have native USB 3.0 support. So apple needn't do any extra work there. Furthermore, not adopting an industry standard is a loss. Adding to that, they haven't gone against USB 3.0 now, have they?
    Why only USB 3.0 in the next-gen Macs? That's Apple's style!
  • Constructor - Friday, September 23, 2011 - link

    Current Intel chipsets don't have USB3 on chip, so it would take external USB3 controllers to add them to a Mac.

    The problem is that such external controllers consume precious PCIe 2 lanes which are comparatively scarce with the mobile Intel CPUs. I've not checked the data sheets, but there may simply not be enough PCIe 2 lanes with a mobile Intel CPU to supply both a full-speed-capable external USB3 controller and the Thunderbolt controller at the same time.

    Given that choice, I'd say Thunderbolt is the far better option of the two (not least since you can connect USB3 externally through it, but not vice versa).

    Desktop CPUs are less constrained, so the iMac and the Mac Pro could have both at the same time even with the current CPU generation (through PCIe plugin cards, if need be).

    But I expect Apple to make the jump with the upcoming CPUs which simply provide them on chip with nothing to sacrifice for it.
  • JasperJanssen - Saturday, September 24, 2011 - link

    Ivy Bridge generation Macs will obviously have USB3. Presumably enough of them so that there are no USB2 ports left, as Apple does not like mix and match. And when the Macs have USB3, the display will get it too. Reply
  • quiksilvr - Friday, September 23, 2011 - link

    Can you use this Thunderbold Display on another Thunderbolt computer that isnt Mac? Reply
  • Anand Lal Shimpi - Friday, September 23, 2011 - link

    Theoretically, yes. We won't know for sure until we see the PC implementations of Thunderbolt but according to Apple if a PC vendor were to integrate Thunderbolt and fully follow the spec the Thunderbolt Display would work.

    Take care,
  • the goat - Friday, September 23, 2011 - link

    Somebody already solved this problem decades ago. It is called a laptop docking station. All those cables you are complaining about stay plugged into the docking station. Reply
  • Parhel - Friday, September 23, 2011 - link

    That's what's confusing me about this too. Why is this better than, or even as good as, a docking station?

    With my docking station, I just have to put my laptop on it, and I'm connected to wired network, monitor, mouse and keyboard. I could add another monitor (2 dual link DVI ports), speakers, a printer, and I believe 4 USB devices to that.

    I have one docking station at home, one at the office. The dock for home cost me under $100, and it's compatible with both my laptop and my wife's. This seems like a step down from that.
  • HMTK - Friday, September 23, 2011 - link

    If you wan't a razor thin laptop like a MBA there's no room for a docking connector in the laptop. That's probably the main reasons why Apple makes this thing. For their customers it's good.

    Personally I prefer a docking station exactly for the reasons you stated. I would like to use a generic docking station that's not USB though because now docking stations can only be used with a limited number of machines and there's no compatibility between brands.

    Laptop makers are being forced by the EU to make compatible power bricks. Why not do the same for docking stations? Or force them to make a single connector for data and power that's also compatible with a power supply only?

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