500MB/min looks like normal 100Mbit. Do not forget that you do not measure pure network performance, but also a disk speed when copying a file.
Actual process looks like READ-TRANSMIT-RECEIVE-WRITE. If both VMs resided on same datastore then you have simultaneous read & write on the same datastore.
You can dismiss write by copying file to NUL. And I suppose you'll get approx 1GB/min, like with physical host.
VMware vExpert '2009
What is the GuestOS, I know Windows 2003 but 32Bit, 64 Bit ? whta is the Virtual NIC in use?
In this case, the affected VMs are 32-bit, and the network adapter is the VMware Accelerated AMD PCNet Adapter.
I did some additional testing, and it looks like disk performance may, indeed, be the ultimate culprit. I'm continuing to check performance characteristics, but it looks like part of the issue is that some of our VMs don't have the correct byte offset at the beginning of their partitions.
In fact, this was the base cause--turns out this makes a huge amount of difference!