[CentOS-virt] Windows Xen VM's have high guest CPU usage and poor performance

Thu Jan 21 17:26:02 UTC 2010
compdoc <compdoc at hotrodpc.com>

>The install worked beautifully except that my VM now has an
ip assigned 
>of which I'm guessing is in relation to
virbr0 which is 
> on the host (and subsequently has no internet

>connectivity).  Is it possible for me to pass through to my
network like 
>before so my VM can have an ip on my local network?

That's the default virtual network that's installed on every
host. It's useful for file transfers, etc. between guests
because it transfers across the host's buses, rather than
across your network switch. I find I have to create a bridge
that's associated with a real/physical network card that can
be shared to the vms. 

If you have only one network card in the server, you should
add more. 32 computers (vms) sharing one card is only one
bottleneck your system has. Another would be using a file to
run the vm from, rather than a block device.

Do me a favor - download the program HD Tach into one of
your XP machines, and when all the other vms are idle, or
turned off, run it and tell me what kind of read/write
speeds you get for the vm's C: drive. I get 200 megs a
second from my 4TB block device, which is 4 sata drives
connected to a 3Ware controller in a raid 5. 

When I read that red hat was going with kvm and might do
away with xen in the future, I decided to install all my vms
using only kvm. And what I found was, that using the built
in virtual hardware for network cards and storage, I get
native speed without having to add the virtio drivers. 

Xen requires a modified kernel on the host machine and
drivers loaded into the vms to get native speeds. That was
always a problem for me because the drivers wouldn't always
load into many linux distros I use.