[fedora-virt] [KVM] Calculation of the number of virtual machines on a single node.

[Richard W.M. Jones]

On Wed, Aug 28, 2013 at 03:24:37PM +0400, Vladimir Parf wrote:
> Hello!
> I'm starting to deploy a private cloud on OpenStack!  As the
> hypervisor I use nova+KVM on Fedora-19.
> Tell me how to count how many virtual machines can be placed on a
> single KVM node.
> How to count the number of virtual machines on single node to get
> everything working perfectly?
> 
> Hardware configuration:
> CPU: 2x  Intel(R) Xeon(R) CPU E5-2609  @ 2.40GHz  - 4 core
> RAM: 96 GB

This is a very open ended question and it will ultimately depend on
your workload, but in general terms it's RAM which is the limiting
factor.  If each guest needs 2 GB of RAM, then you might fit ~40 VMs
on this machine (I'm allowing about 512 MB overhead per guest).

8 cores would seem to be sufficient, unless every guest needed to do a
lot of compute-intensive work at the same time.

> HDD:Unlimited
> HW: ProLiant BL460c

Unlimited?  Storage size is probably not a concern, but bandwidth to
storage definitely matters, particularly if you're really going to try
running 40 guests and they're all hitting disk frequently.  If you
thought about this in terms of having 40 physical machines all sharing
a disk, then you'd need a medium-performance SAN, and the same would
be true of 40 virtual machines.

Basically .. you need to measure it, using all the normal performance
tools on the host.

Rich.

-- 
Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones
Fedora Windows cross-compiler. Compile Windows programs, test, and
build Windows installers. Over 100 libraries supported.
http://fedoraproject.org/wiki/MinGW