[libvirt-users] VM Performance using KVM Vs. VMware ESXi

Tue Apr 14 20:51:34 UTC 2015

Hi Jatin,

The RedHat documentation on this is extremely helpful. It's so helpful that
I use it as a reference on completely different distributions.

VMWare does a pretty good job of guiding you and giving you defaults that
are sensible. With Libvirt/QEMU/KVM, you need to get an idea of those and
enable them yourself.

For example, I see that you are using qcow2 files, but if you don't need
the features it provides, then using block devices (usually logical volumes
in a volume group) directly for VM disks may be significantly faster. It
also depends on how caching is configured. The manuals will step you
through all of that. Pay special attention to storage, because it's the
first bottleneck a lot of applications hit.

Check out the manuals under the virtualization section here:
https://access.redhat.com/documentation/en-US/Red_Hat_Enterprise_Linux/

Specifically:
https://access.redhat.com/documentation/en-US/Red_Hat_Enterprise_Linux/7/html/Virtualization_Tuning_and_Optimization_Guide/index.html

Good luck!
Nikki

On Tue, Apr 14, 2015 at 9:18 AM, Matt Schumacher <matt.s at aptalaska.com>
wrote:

>  Jatin,
>
> Using qemu without the virtio scsi and nic drivers is like running vmware
> with ide disks and e1000 nic instead of LSI disks and vmxnet3 nics, it
> forces the system to emulate completely different hardware.
>
> In linux the virtio drivers are implemented in the kernel, so you either
> need a new kernel or the virtio kernel modules.  I'm not sure which for
> RHEL5, but I suspect you can get what you need with the kmod-virtio
> package, then rebuilding the initrd image to load the modules at boot.
>
> Keep in mind that sda will change to vda, which on some linux distros
> requires updates to the bootloader and inittab, but redhat uses filesystem
> labels if I remember correctly, so it should just work.
>
> Please let us know how the benchmarks look after you get virtio working,
> I'm curious...
>
> schu
>
>
>
> On 4/14/2015 5:33 AM, Jatin Davey wrote:
>
> Thanks Dominique & Daniel.
>
> Looks like i need to upgrade my VMs kernel to make it aware of virtio.
>
> Found this information from this link:
>
> http://wiki.libvirt.org/page/Virtio#Disk_.28block.29_device_driver
>
> I tried without upgrading the Kernel and as soon as i start my VM it got
> into Kernel Panic. I will try using virtio after upgrading my VMs kernel.
>
> Thanks for all the responses and pointers.
>
> Thanks
> Jatin
>
> On 4/14/2015 5:08 PM, Dominique Ramaekers wrote:
>
> Please read: https://libvirt.org/formatdomain.html
>
>
> -----Oorspronkelijk bericht-----
> Van: Jatin Davey [mailto:jashokda at cisco.com <jashokda at cisco.com>]
> Verzonden: dinsdag 14 april 2015 13:39
> Aan: Daniel P. Berrange
> CC: Dominique Ramaekers; libvirt-users at redhat.com
> Onderwerp: Re: [libvirt-users] VM Performance using KVM Vs. VMware ESXi
>
> On 4/14/2015 4:58 PM, Daniel P. Berrange wrote:
>
>  On Tue, Apr 14, 2015 at 04:53:52PM +0530, Jatin Davey wrote:
>
>  On 4/14/2015 4:42 PM, Dominique Ramaekers wrote:
>
>  About Spice: I think it’s good practice to use spice because it
> improves the performance of the VM in general by improving screen
> performance. If your VM is constantly displaying output, you’ll
> probably will notice a difference.
>
>
>  [Jatin] Ok, This is not my concern as of now. I will take a look at
> it sometime later.
>
>  About virtio: You can see it in the settings. Better yet, it’s in
> your XML. If you post your XML, we can take a look…
>
>
>  Here is the xml associated with my VM:
>
> ********************************
> <domain type='kvm'>
>    <devices>
>      <emulator>/usr/libexec/qemu-kvm</emulator>
>      <disk type='file' device='disk'>
>        <driver name='qemu' type='qcow2' cache='none'/>
>        <source file='/var/lib/libvirt/images/****.qcow2'/>
>        <target dev='hda' bus='ide'/>
>        <address type='drive' controller='0' bus='0' target='0' unit='0'/>
>      </disk>
>
>  This disk is configured to use IDE, so performance of anything that
> does disk I/O is going to be terrible. You really want to be using virtio.
>
>
>      <interface type='bridge'>
>       <mac address='52:54:00:c9:58:c9'/>
>       <source bridge='br332'/>
>       <address type='pci' domain='0x0000' bus='0x00' slot='0x03' function='0x0'/>
>      </interface>
>
>  This doesn't have any model listed at all, so it will be falling back
> to a generic emulated NIC. Again performance of this is likely going
> to be terrible for anything doing network I/O. You want to be using
> virtio for this too.
>
> Regards,
> Daniel
>
>  How do i make use of virtio for the both disk and network that you have mentioned above ?
> Any pointers to it would be helpful.
>
> Thanks
> Jatin
>
>
>
>
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-- 
Nikki VonHollen
Goobuntu Team <https://goto.google.com/goobuntu>
540-553-1904
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