[ovirt-users] Bad performance with Windows 2012 guests

[Martijn Grendelman]

Hi,

Ever since our first Windows Server 2012 deployment on oVirt (3.4 back 
then, now 3.5.1), I have noticed that working on these VMs via RDP or on 
the console via VNC is noticeably slower than on Windows 2008 guests on 
the same oVirt environment.

Basic things like starting an application (even the Server Manager that 
get started automatically on login) take a very long time, sometimes 
minutes. Everything is just... slow.

We have recently deployed Microsoft Exchange on a Windows Server 2012 
guest on RHEV, and it doesn't perform well at all.

I haven't been able to find the cause for this slowness; CPU usage is 
not excessive and it doesn't seem I/O related. Moreover, other types of 
guests (Linux and even Windows 2008) do not have this problem.

We have 3 different environments:
- oVirt 3.5.1, on old Dell servers with Penryn Family CPUs with fairly 
slow storage on replicated GlusterFS, running CentOS 6.6
- oVirt 3.5.1, on modern 6-core SandyBridge servers with local storage 
via NFS, running CentOS 7.0)
- RHEV 3.4.4 on modern 10-core SandyBridge servers with an iSCSI SAN 
behind it, running on RHEV Hypervisor 6.5

All of these -very different- environments expose the same behaviour: 
Linux, Windows 2008 fast (or as fast as can be expected given the 
hardware), Windows 2012 painfully slow.

All Windows 2012 servers use VirtIO disk and network. I think all 
drivers are from the virtio-win-0.1-74 ISO.

Does anyone share this experience?
Any idea why this could happen and how it can be fixed?
Any other information I should share to get a better idea?

Btw, for the guests on the RHEV environment, we have a case with RedHat 
support, but that doesn't seem to lead to a quick solution, hence I'm 
writing here, too.

Thanks for any help.

Regards,
Martijn Grendelman