libvirt users - May 2013 - Usual number of guests on a host

Hi,
  Can someone tell us what is the usual number of guests on a typical host in a
production environment ? Has someone tested this ? What number does it scale to
? We have around 150 per host running fine.

Regards,
Navin

On 05/28/2013 06:07 AM, Parakkal, Navin S wrote:
> Hi,
>   Can someone tell us what is the usual number of guests on a typical host
in a production environment ? Has someone tested this ? What number does it
scale to ? We have around 150 per host running fine.
It all depends on how beefy your hardware is, and how much you are
willing to oversubscribe on memory to run your guests.  It is quite easy
to run more than one single-vcpu guest per processor, although you may
need NUMA pinning to help that setup run efficiently; at least until you
run into kernel limits of what KVM can do (for example, while you were
able to run 150 guests, you might hit some sort of boundary at 256 or
512 guests according to how guests are represented in the kernel).
Personally, I don't have a machine that beefy to tell you any hard
numbers.  If you really want to discuss scalability, you may be better
off remembering that upstream is best effort only.  If you need hard
answers or guarantees for your particular setup, you may want to
consider using an enterprise solution; for example, Red Hat has specific
numbers of how many guests are supported on RHEL, along with benchmarks
to back up their claims.

-- 
Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org

>   Can someone tell us what is the usual number of guests on a typical
> host in a production environment ? Has someone tested this ? What number
> does it scale to ? We have around 150 per host running fine.
It obviously depends on your virtualization backend, host, memory, disk,
NIC etc. So I'm not sure what you're after.

I'm pretty much sure I could easily create something like 10k virtual
machines running DOS or something like that on a box with 16GB memory;
however, I doubt that it would be useful.

On the other hand, this might be a nice test to see how well the libvirt
tools handle things.

Felicitus