Back to the Mac 010: Dual eGPUs!

Back to the Mac is a series focused specifically on the Mac, including hardware, accessories, I/O, software, and more.

On this week’s episode of Back to the Mac, we go nuts with an eGPU setup featuring two Sonnet eGFX Breakaway Box 650 units mated with a pair of workstation-class 16GB AMD WX 9100 GPUs.

As we’ve touched on before, if you’re a DaVinci Resolve user, or if you use any other app that can wield multiple GPUs at the same time, such a setup can put up some noteworthy numbers. Watch the latest episode of Back to the Mac for more details.



It’s no surprise that a dual eGPU setup can significantly improve export performance in DaVinci Resolve. In fact, we tested such a setup a few months ago, to confirm the performance improvements.

But I’ve long wanted to test a MacBook Pro with a faster setup involving two identical eGPU setups. For this test, I’m using a pair of Sonnet eGFX Breakaway Box 650s, which Apple specifically recommends as the most powerful and versatile eGPU chassis for the Mac. Both chassis’ are mated with identical Radeon Pro WX 9100 GPUs, workstation-class Vega 64-based cards, that Apple specifically notes as a pairing option with Sonnet’s high-end graphics enclosure.

I learned something new while filming this episode: the 2018 MacBook Pro can handle up to four eGPUs — two eGPUs per Thunderbolt 3 bus — simultaneously. On the MacBook Pro, or iMac Pro you can connect eGPUs to any of the available Thunderbolt 3 ports. I briefly dabbled around with connecting four eGPUs to my MacBook Pro, and needless to say, it was downright absurd. If you’d like to see more about that, let me know down below in the comments.

The most obvious application to test when working with more than one eGPU is the paid version of DaVinci Resolve, DaVinci Resolve Studio. That’s because Blackmagic Design’s powerful NLE heavily relies on the GPU and supports multiple GPUs with a simple configuration change. DaVinci Resolve Studio is thus the perfect application to showcase how much of an effect an eGPU can have on creative professional workflows.

As I said, configuring multiple eGPUs in DaVinci Resolve Studio is easy. If you go to Preferences → System → Hardware Configuration, you can choose to manually select the GPUs you wish to use. In the screenshot below, you can see how DaVinci Resolve Studio recognizes both AMD Radeon Pro WX 9100 GPUs, and I’ve enabled both.

Once you configure the GPU settings, a simple app restart is all that’s required for DaVinci Resolve to begin using them.

The results, as I’ve alluded to, are quite evident in both timeline perusal and delivery. Here’s a graph showing how much export times improved when using one or two Radeon Pro WX 9100s:

In the above benchmarks, I exported a 15 minute and 15 second 24p UHD clip using H.264 with a 45000 Kbps bitrate.

Exporting the project with no effects showed considerable improvements when wielding an external GPU, going from 2520 seconds or about 42 minutes, to around 584 seconds, or just a little under 10 minutes. Now imaging having to repeat such a process day in and day out, and you can see how big of a time savings an eGPU can make.

Unsurprisingly though, what really stands out is eGPU performance improvements on effects-laden timelines. I inundated my 15 minute and 15 second clip with a laughable amount of GPU-accelerated OpenFX effects — Vortex, Dent, Waviness, Camera Shake, Film Grain, JPEG Damage, Abstraction, Sharpen, and Light Rays — causing the integrated GPU to completely fall down. With eGPU assistance, playback, editing and exporting featured no frame drops. This tells me that it’s pointless to try to edit effects-heavy timelines in DaVinci Resolve without discrete GPU acceleration, something that 13-inch MacBook Pro models lack.

But I don’t want to make the mistake of concentrating solely on delivering video, because the actual editing process is greatly improved when using an external GPU as well. For example, on my timeline where I applied the aforementioned effects, playback of a 24 fps project crawled around 2-4 fps when using the integrated GPU, and you can forget about using J-K-L commands to quickly move about the timeline.

When using one or more WX 9100s, timeline perusal is quick and snappy, with playback immediately occurring at full speed as soon as the playhead touches down.

This dual eGPU setup supercharges my base model 13-inch 2018 MacBook Pro when it comes to working with single projects with tons of effects, but what if you paired such a setup with a beastly machine like the iMac Pro? As you probably guessed, lots of good things happen with video workflows.

Because the Vega 64 architecture features an asynchronous compute engine, it allows you to easily multitask and stay productive even while other GPU-intensive tasks are running at the same time.

To test this out, I opened up multiple instances of DaVinci Resolve Studio 14 — three in all — and was able to play back three 4K streams simultaneously without dropping frames. Some of these 4K timelines even had several effects applied, yet playback remained smooth. Keep in mind that this occurred when using two Sonnet eGFX Breakaway Box 650W’s. I imagine that having four eGPUs would yield an even higher ceiling to work with.

Running three instances of DaVinci Resolve Studio may sound excessive, but it means that you can easily manage multiple projects at once. For example, you could be exporting a project, coloring another, and cutting still another.

Trying to do the same when using the iMac Pro’s built in GPU, or even a single WX 9100 resulted in some frame drops, but having two WX 9100s makes a noticeable difference in performance depending on the type of timelines and effects that you’re dealing with.

To further test the potency of this dual WX 9100 setup, I ran a few LuxMark OpenCL tests, which let you choose one more GPUs to bench. Have a look at the LuxMark results:

As expected, a single eGPU considerably increases OpenCL performance, while a dual GPU setup makes an even greater difference, more or less doubling a single eGPU.

We’re still in the early days of eGPU support on the Mac, but already, the technology has grown by leaps and bounds. If you’re a DaVinci Resolve user, then you stand to yield massive gains from an external graphics chassis. And with Apple continuing to focus on improving the way eGPUs work with its machines, I imagine that many more apps will seek to take advantage of external graphics on the Mac.

Special thanks to Sonnet and AMD for working with me on this exercise. They provided the eGPU enclosures and GPUs for me to test out the performance of this dual external graphics setup.

What do you think about running one or more eGPUs with your Mac? Leave your thoughts in the comments below.


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