Windows file copy fast in one direction but much slower in the reverse direction between 2 servers.

Hi all,

Have an interesting problem, I have 2 identical servers, both of them running MS Windows Server 2003 R2 Enterprise x64 SP2 with all the latest patches / updates. Using FastCopy (basic windows file copy) to copy large files (>1GB) between them, going from

server A -> server B : transfer rate ~ 10MB/s

BUT, going from

server B -> server A : transfer rate ~ 3-4MB/s

As a 'control' I've also tested transfer rate from and to each server A and server B to another server C and there are no issues (fast transfer rate ~10MB/s).

server A <-> server C; server B <-> server C : no issues!

Now assuming the network environment is functioning 100% (ie. no dropped/duplicate packets, no protocols in between, etc) what are some possible causes on the systems for this unusual behavior? Why the huge difference in transfer rate between the 2 directions?

I've played around with TCPWindowSize and saw maybe a very slight improvement ~1-2MB/s. Are there any other tweaks that may be done?

Thanks!

-Dave