[mgerdts]

Robocopy has options for unbuffered IO (/J) and parallel operations (/MT:N) which could make it go much faster.

Performing parallel copies is probably the big win with less than 10 Gb/s of network bandwidth. This will allow SMB multichannel to use multiple connections, hiding some of the slowness you can get with a single TCP connection.

When doing more than 1-2 GB/s of IO the page cache can start to slow IO down. That’s when unbuffered (direct) IO starts to show a lot of benefit.

[hiAndrewQuinn]

The strange thing is, I did have /MT:32 on (added in a comment at the bottom of the page because I had to go to bed). I like to stick with defaults but I'm not that inept. /J probably shouldn't matter for my use case because 125 MBps just isn't that much in the grand scheme of things.