On some servers (not all), after installing paravirtualized drivers in a Xen guest domain on Windows (Server), throughput over a network "share" drops to almost zero (a few KB/s). At the same time, the speed on emulated QEMU drivers (HVM) is normal.
The effect may not be immediately obvious, because the guest machine itself works fine (i.e., if you log in via RDP or connect through the console and work with the network - everything is fine, the speed is excellent), but if you try to access this virtual machine's file system from the outside via Windows shared resources (from any other computer), you get an extremely low speed, comparable to a modem (or even lower).
So what should you do?
There are 2 options:
1) Go back to HVM. But this will negatively affect disk operation speed and other aspects, and the network speed there isn't great anyway.
2) The tastiest option: Go to the Xen network adapter settings, to the "Advanced" tab, and there you'll see the "Large Send Offload" parameter. By default its value is 61440. Remove this value and set it to "Disabled". Then close the properties dialog - and voila! Our network interface speed has increased significantly. According to my measurements, on a 100Mbit/s interface I got 9-10MB/s, meaning the losses are greater than with "Large Send Offload", but unfortunately this feature itself doesn't work with all hardware and Linux drivers, so at least this works.
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