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I'm trying to figure out what's going on. I've got a Mac Pro connected with a Sonnet Twin 10G adapter to a Windows 10 PC with a StarTech 10G PCI card. If I try and transfer a file, I get about 350MB/sec. If I do an iperf test (and set the TCP window really high), I get much higher:

[ ID] Interval           Transfer     Bandwidth
[  5]   0.00-1.00   sec  1.11 GBytes  9.50 Gbits/sec
[  5]   1.00-2.00   sec  1.15 GBytes  9.88 Gbits/sec
[  5]   2.00-3.00   sec  1.15 GBytes  9.89 Gbits/sec
[  5]   3.00-4.00   sec  1.15 GBytes  9.89 Gbits/sec
[  5]   4.00-5.00   sec  1.15 GBytes  9.89 Gbits/sec
[  5]   5.00-6.00   sec  1.15 GBytes  9.88 Gbits/sec
[  5]   6.00-7.00   sec  1.15 GBytes  9.89 Gbits/sec
[  5]   7.00-8.00   sec  1.15 GBytes  9.88 Gbits/sec
[  5]   7.00-8.00   sec  1.15 GBytes  9.88 Gbits/sec
- - - - - - - - - - - - - - - - - - - - - - - - -
[ ID] Interval           Transfer     Bandwidth
[  5]   0.00-8.00   sec  0.00 Bytes  0.00 bits/sec                  sender
[  5]   0.00-8.00   sec  9.73 GBytes  10.4 Gbits/sec                  receiver

I've turned on Jumbo Frames and set the MTU to 9000 on both devices. No matter what I do I can't get over 350MB/sec on a file transfer. I'm trying to get this above 700MB so I can stream 4K video to my editing software.

Any other suggestions? From my tests, it looks like the connection is capable of 10G but for some reason something in macOS Sierra or Windows 10 is limiting the speed.

Beta4
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    Have you considered your disk architecture/transfer rate? This looks like the SATA II transfer rate –  May 23 '17 at 12:36
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    I've set both sides to have a RAM disk to remove any drive speed limits. No change. I've got a SATA III SSD and as well as an NVMe SSD. –  May 23 '17 at 13:00
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    Not considering cabling or other factors, SATA III SSD transfer will likely max at about 500MB (in fact, theoretical limit is 600MB). See [SanDisk Difference between SATA I, SATA II and SATA III](https://kb.sandisk.com/app/answers/detail/a_id/8142/~/difference-between-sata-i%2C-sata-ii-and-sata-iii). In any case, probably not so much a "networking" issue as your ability to get data to/from the network –  May 23 '17 at 13:06
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    Right but if I'm using a RAM disk, then SSD limits are removed. As mentioned above, the iperf shows fine. It's just something with macOS or Windows 10 file transfers or something with the network mount. –  May 23 '17 at 13:11
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    What is the file transfer protocol? – Aaron May 23 '17 at 13:21
  • Default when mapping a drive on windows 10. SMB. – Beta4 May 24 '17 at 11:41
  • It appears in [this thread](https://superuser.com/questions/74000/whats-the-typical-performance-of-windows-file-sharing-smb-on-a-gigabit-ethern) someone determined that SMB is CPU bound to a single core. As an experiment, you might try a multi-threaded or multi-forked web server. Maybe fire up apache or nginx on your mac as an experiment. – Aaron May 24 '17 at 13:07
  • That's not the case with SMB3 – Beta4 May 24 '17 at 13:52
  • And [this](https://arstechnica.com/civis/viewtopic.php?t=1305827) article is specific to SMB3 and Mac. You might give those tips a shot. Without performance numbers from both your windows and mac machine anything here will be guessing. – Aaron May 24 '17 at 14:48
  • Through some tweaks I was able to get the performance to about 850MB/s on a large file and about 350-400MB/s on a large amount of smaller files. Still using the RAM disks. Anything else to tune to get smaller files to transfer as fast as the larger? – Beta4 May 24 '17 at 15:47
  • You might run bonnie++ HD benchmarking on your mac and windows machines to see if those numbers align with your recent results. – Aaron May 24 '17 at 16:12
  • HD tests on the ram drive I'm using show 3000+ (testing locally on each to their ram drive) – Beta4 May 24 '17 at 21:11
  • I think at this point you would have to start investigating different sysctl and ifconfig tuning options for the mac and registry tweaks for windows to make more use of the bandwidth. Perhaps someone has done a big write-up on that here. I mostly review serverfault questions, so unsure if such a write-up exists here. – Aaron May 24 '17 at 22:32

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