Hi guys, I’m new here and thought I’d just write a solution.
Because I’m sure some of you will have this problem today.
So, I set up my new My Cloud Ulta 16TB and started robocopy right away.
Copy data. That didn’t work at first and I (IT-Professional) had to understand what was going on. Even on the internet you don’t find it that easy.
I have here 3 switches GS108T, which is however surely not the problem, would occur with others surely also. There were network errors, which are not very helpful from Windows mostly: Error 0x8007003b and others.
The problem was the packet size, not only for the WD, but of course everywhere where the IP packets have to be long, so also for the switches and Windows TCP drivers!
So if you have the problem that Windows hangs, or something like that, think of these words 
If you take this into account, you get 120MB/s over 2 switches like me here, that’s about 984MBit/s, so I think the values are very good, because the network card is used almost completely. I have set the packet size for all stations to 9K.
I have now still converted this into English, was not at all so conscious to me that here also everything is English.
Best regards from Berlin
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