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Are all TB3 ports full speed on my MacBookPro15,2?
 

Are all TB3 ports full speed on my MacBookPro15,2?  

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Swisher Sweet
(@swisher-sweet)
Eminent Member
Joined: 3 years ago
 

I'm wondering if I connect my eGPU to any of the 4 ports on my 2018 MacBook Pro (MacBookPro15,2), if all 4 ports operate at the same speed?

Under System Information, I see two TB busses (Bus 0 and Bus 1). Each bus as two "ports" with a "Speed" that is specified as "Up to 40 Gb/s x1".

So are all 4 of the TB3 ports equal?

Thank you.

2018 13" MacBook Pro
Razer Core X Chroma (don't but this if you use a Mac)
AMD Radeon VEGA 64
Dell UltraSharp u3415w


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itsage
(@itsage)
Illustrious Member Admin
Joined: 3 years ago
 

The two Thunderbolt 3 controllers and four Thunderbolt 3 ports are equal in your specified MacBook Pro model. They all have a theoretical max bandwidth of 40Gbps. Given the same enclosure, GPU, and cable the performance should be the same if you connect the eGPU to any of the four TB3 ports.

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Swisher Sweet
(@swisher-sweet)
Eminent Member
Joined: 3 years ago
 
Posted by: @itsage

The two Thunderbolt 3 controllers and four Thunderbolt 3 ports are equal in your specified MacBook Pro model. They all have a theoretical max bandwidth of 40Gbps. Given the same enclosure, GPU, and cable the performance should be the same if you connect the eGPU to any of the four TB3 ports.

Thanks for the reply. Curious, if I were to connect an eGPU to one port, and a TB3 NVMe drive to another port, should I use specific ports to get the best throughput? For example, would I get best performance by splitting the two devices between two different buses? That is, one device on left side, one device on right side?

Thanks again!

2018 13" MacBook Pro
Razer Core X Chroma (don't but this if you use a Mac)
AMD Radeon VEGA 64
Dell UltraSharp u3415w


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joevt
(@joevt)
Prominent Member
Joined: 2 years ago
 

@swisher-sweet Yes, two busses is better. Ignoring DisplayPort bandwidth, each port is limited to 22 Gbps and each bus is limited to 23 Gbps. There are separate lanes for read and write. If a display is connected at the end of a Thunderbolt chain, then it will limit write speed if the display requires more than 40 - 22 = 18 Gbps.

Mac mini (2018), Mac Pro (Early 2008), MacBook Pro (Retina, 15-inch, Mid 2015), GA-Z170X-Gaming 7, Sapphire Pulse Radeon RX 580 8GB GDDR5, Sonnet Echo Express III-D, Trebleet Thunderbolt 3 to NVMe M.2 case


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Swisher Sweet
(@swisher-sweet)
Eminent Member
Joined: 3 years ago
 

@joevt

Thanks for the clear explanation. I didn't realize the display port took up all that bandwidth. That would explain why you only get a max of 2,750 MB/s theoretical max on external NVMe drives.

So for my situation, I'd get the best performance if I connected my eGPU to one side of the Mac (bus 0) and the NVMe drive to the other side of the Mac (bus 1).

Thanks again!

This post was modified 5 months ago

2018 13" MacBook Pro
Razer Core X Chroma (don't but this if you use a Mac)
AMD Radeon VEGA 64
Dell UltraSharp u3415w


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joevt
(@joevt)
Prominent Member
Joined: 2 years ago
 
Posted by: @swisher-sweet

That would explain why you only get a max of 2,750 MB/s theoretical max on external NVMe drives.

No it doesn't because 2750 MB/s or 22 Gbps is the max without DisplayPort connected - DisplayPort doesn't reduce Thunderbolt PCIe bandwidth unless you connect a display after a Thunderbolt device and only if the display requires more than 18 Gbps. A single 4K display only requires 16 Gbps. There is no explanation for why Intel limits PCIe bandwidth to 22 Gbps. I wonder if USB4 will change that limit (when third parties start making USB4 controllers).
https://thunderbolttechnology.net/sites/default/files/Thunderbolt3_TechBrief_FINAL.pdf

Mac mini (2018), Mac Pro (Early 2008), MacBook Pro (Retina, 15-inch, Mid 2015), GA-Z170X-Gaming 7, Sapphire Pulse Radeon RX 580 8GB GDDR5, Sonnet Echo Express III-D, Trebleet Thunderbolt 3 to NVMe M.2 case


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