MacBook Air 2020 wifi performance

[citivolus]

I've noticed some strange behavior while testing network performance. While connected to an 802.11ac router that supports AC1300, my upload speed is roughly double the download speed on my LAN. Testing performed with both iPerf 3 and also straight file copy from the MBA to my gigabit-wired iMac. Copying a 2GB file to the iMac reaches almost 1Gb/sec whereas copying a file from the iMac to the MBA achieves only 500Mb/s. Anyone have an idea why this is happening? Both are running Catalina.

 

[twintin]

No idea. Mine has pretty much same upload as download, at least in speed tests. However I only have a 5:th gen Air Port Base station.

 

[deeddawg]

Does the iMac have a fusion drive?

Could it be caching the write to the iMac within the SSD portion and thus that direction appears faster?

 

[citivolus]

Does the iMac have a fusion drive?

Could it be caching the write to the iMac within the SSD portion and thus that direction appears faster?

No it has an ssd and an internal spinning hd. I’ve tested reading/writing to each one and gotten similar results.

 

[deeddawg]

No it has an ssd and an internal spinning hd. I’ve tested reading/writing to each one and gotten similar results.

Oh well. Just a thought.

 

[citivolus]

I was really determined to get to the bottom of this. After a lot of testing, I've found a bug in Catalina that is causing this behavior. Seems that macOS is double-counting the network traffic uploaded by a wifi connection. This can be confirmed by doing a simple internet speed test. My internet connection is 50Mbps/50Mbps. When I run the speed test on my 2017 MacBook running Mojave, it correctly shows the same upload and download speed in the Network tab of Activity Monitor. When I run the same speed test on my 2020 MacBook Pro and 2020 MacBook Air which are running Catalina, the "Data sent/sec" value is double what it is on my other devices, which obviously is incorrect as my internet speed is fixed. Guess it's time to file a bug report.