I am having an issue that I cannot figure out. The short version is, if I copy a file FROM a Windows 2012R2 server to a Windows 7 client across a 10Mbps MPLS, the performance is terrible. It sits there and "calculates" for about 10 seconds before it does anything, and then it starts slowly copying, eventually reaching about 5Mbps. Ironically enough, if I copy the file TO the Windows2012R2 from the Windows 7 PC, it works normally, copying starts immediately and stays consistent at 10Mbps the entire time.
I can copy the same file from the same Windows 2012R2 server from a Windows 7 PC that is on the same physical LAN, and it copies at wire speed (100Mbps) instantly.
To rule out the MPLS being the problem, I can copy the same file between Windows 7 clients at both sites on the same MPLS and it always works perfectly (10Mbps) whether copying to or from.
For double good measure, I've run IPERF and get consistently good results using IPERF. So all signs point to an SMB problem, but I can't figure out what it is. Things I have tried: the NIC drivers are up to date on everything. I've done the usual "turn off Receive Side Scaling, Chimney, Offload, etc" on the NIC in the server, nothing made any difference. I forced SMB1, that didn't help. I did take a packet capture in Message Analyzer and it appears to me that there are a lot of re-transmissions, duplicate ACKs, and packets arriving out of order. Again, though, it can't be the MPLS because Windows 7 - Windows 7 copies across the same MPLS are perfect.
I'd appreciate any suggestions or experiences you could share as I am really stumped. Thanks in advance.