[Openstack] [OpenStack][KVM] Calculation of the number of virtual machines on a single node.

josh at kleinpeter.org josh at kleinpeter.org
Wed Aug 28 11:44:29 UTC 2013

That depends on how big the VM is, and what over subscription rate you're running out.

Generally RAM is going to be your limiting factor, it is fairly easy to over subscribe CPU, and if you're disk is really unlimited, that isn't going to stop you either.

Assuming you're not oversubscribing RAM, you'll need to account for the overhead of your operating system and various services, KVM overhead etc, say 8-12GB. Subtract that out of your RAM number. 

Then divide by the amount of RAM your base VM has, and that would be how many you could (theoretically) run. Your CPU over subscription rate would then play in as a factor of how many of those is really possible.

More importantly -- try it out and see where it breaks! Nothing like a good load test.

> Hello!
> I'm starting to deploy a private cloud on OpenStack!  As the hypervisor 
> I use nova+KVM on Centos 6.4.
> 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
> HDD:Unlimited
> HW: ProLiant BL460c

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