10G ethernet on both machines connected both into UDM Pro ports.
windows WSL → truenas: 4.68 Gbits/sec
truenas → Windows WSL: 800 Mbits/sec
Clearly, the bits flow faster downhill than uphill 
My windows box has SSD, truenas has CMR drives and 128GB of cache.
Thought people might find these numbers interesting.
The transfer rate is measure with 1 second of transfer time so that means truenas didn’t have to write anything to the disk over that period since it caches up to 5 seconds in RAM.
iperf3 doesn’t read from or write to any drives or storage devices.
It actually has that as a new feature! But only if you ask for it.
On Windows you might get better results with iperf2. Iperf3 isn’t an “upgrade”, it’s a completely different platform. Historically iperf3 hasn’t had great performance on Windows - recent versions are better, but still …
That includes an excerpt from the iperf3 FAQ where they recommend using iperf2 on Windows.
I haven’t tried the Microsoft ntttcp tool on Linux (or FreeBSD).
yeah, figured that out pretty quickly…
It’s interesting that the rates are NOT symmetric. Why is that???
I was running iperf3 from Debian in WSL.
I expected performance should be same in both directions, but it surprisingly wasn’t!
