Windows Guest - Huge network speed slowdowns

[fxandrei]

I have a windows server 2008 r2, with raw disk, and virtio network card.
I have a NAS from where i try to copy certain things (big things).
I have gigabit all around.
Every time i try to copy something big (like 5-20 gb file), it starts great, with 60-80 MBps but after about 2gb coppied i get a huge slowdown.
I slows down to a couple of megabytes per second, even below 1mb.
After a while i get another "burst" of 10-20 seconds, but a slower speed (20mpbs or less), than it slows down again, and so on.
I tested copying stuff from other vm on the same server, and i dont have any problems (centos/debian/ubuntu). It copies the files with 50-90 mbps .
I dont know what is happening with Windows guest (i tryied with fresh win7 vm, and it behaves the same with virtio or e1000).

I really dont know what is wrong.

 

[fxandrei]

Sooo..
I went into the windows guest and started resource monitor.
It seems that the disk is at "100% Hightest Active Time" and the cpu is "100% Maximum Frequency".
Why ? What can i look at ? How could i determine what is causing this ?

 

[fxandrei]

Im back.
After extensive reading and digging around i found the solution.
Ive set the hard drive cache mode to "Write Back".
Everything is perfect now. I dont get those huge slowdowns anymore.