Open Stack

On Thu, Jan 9, 2014 at 9:17 AM, Mridhul Pax <mridhul at live.com> wrote:
> Hello Stackers,
>
> Any one using KVM as hypervisor in the production servers ? We are planning
> to use KVM as hypervisor in our production systems and we are planning to
> use 5 hypervisor nodes (~40 vms per hypervisor).

I have 60 hypervisor nodes running kvm and consider my site on the
small side of medium.

The number of VMs per hypervisor is a very tricky question, a better
though no less tricky question is the ratio of physical CPUs to
virtual CPUs.  This is much more a function of you expected work load
than the hypervisor you choose.

For compute intensive workloads we schedule 1:1, for random webhosting
type loads we've run up to 9:1 and still had the physical systems 80%
idle.  In practice our mixed development/research environment (which
is what we do http://www.csail.mit.edu) seems to run best at 3:1 or
4:1. So our physical nodes are dual socket hex core with
hyperthreading enabled so they present 24 'cpus' (threads really) to
the hypervisor and max out with our work loads hosting 72 to 96 vCPUs.
 We find memory availability is currently our more limiting factor.
We do keep a separate set of nodes (a host_aggregate in openstack
terms) scheduled 1:1 for pure compute instances, if those were mixed
with the general compute we'd need to significantly reduce our
allocation ratios

> How scalable is KVM when used with openstack ? Any limitations ?

I'd say given opensstack's architecture the hypervisor choice doesn't
impact horizontal scale out at all, though I'm only really familiar
with Xen and KVM but I'd really be surprised if other hypervisors
impacted the number of compute nodes you could deploy with them.

> Any ideas on handling HA (live migration) and Storage Motions ?
>
> Is there a way I can restrict IOPS per VMs ?

I'm not currently doing either of these so I'll leave the answer to
others, pretty sure they're both possible

> Which Hypervisor is recommended to use with Openstack ?

That's pretty much the same as asking what the best hypervisor is.

A reasonable answer is "the one you're most familiar with".  A better
answer would be to test your workload on a variety of hypervisors and
see which works best for the load and features you need.  Performance
wise they will be the same inside or outside OpenStack.  I think most
hypervisors have pretty good feature coverage in OpenStack but it's
not inherent so if a feature is important you should look in the
OpenStack docs and see it's exposed.

Popularity is also a consideration in that more popular choices tend
to have better support because more people work on them and you're
more likely to get responses to questions from the larger user
community. http://www.openstack.org/summit/portland-2013/session-videos/presentation/openstack-user-committee-update-and-survey-results
has results of the latest User Survey if you're interested in what's
popular (hypervisors are on slide 16, KVM is used by 71% of
respondents)

-Jon