[libvirt-users] How to best I/O performance for Window2008 and MSSQL guest VM

Blair Bethwaite blair.bethwaite at gmail.com
Tue Dec 6 05:06:37 UTC 2016

Hi Roberto,

What is the cpu and memory configuration of your guest? Are you
pinning to dedicated CPUs, are you exposing host topology and cpu
features, do you have dedicated I/O threads? Are you backing the guest
memory with hugepages? All of the above will likely increase
performance and minimise noise.


On 6 December 2016 at 05:13, Roberto Fichera <kernel at tekno-soft.it> wrote:
> Hi There,
> I've moved some Windows2012 with MSSQL VMs from an hold ESXi 5.5 machine
> to a more recent and powerful machine running Fedora 24 x86_64 and related libvirt + KVM
> virtualization. I've moved the VMs filesystem to LVM slices and installed the VirtIO drivers
> in to all Windows VMs. I've also set both Disk and Network interface to work using VirtIO.
> So far so good everything works pretty fine. Now I would like to tune at best the MSSQL VM
> for both Disk and Network interfaces in order to get the best performance possible.
> Regarding network interface I've set it to work as bridge instead to go through to macvtap, so I'm
> not sure what is the best in this case.
> Regarding disk, since it's LVM I've chosen to go to cache mode none and IO mode native. Also
> here cannot judge what's the best setup for the workload. I'm undecided to use IO mode threads
> along directsync cache mode.
> Finally I've set "ionice -c 1 -p <qemu-pid> -n 0" and "renice -n -10 <qemu-pid>" for the interested
> VM that I want to get best performance possible.
> Even with the above setup, the MSSQL VM has performance similar to the old machine running
> ESXi 5.5, so does anyone can suggest where too look at and/or what would be the right setup?
> Thanks in advance.
> Roberto Fichera
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