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maximum no of VMs on 8 Core machine - Best Practice

Valued Contributor

maximum no of VMs on 8 Core machine - Best Practice

Non Linux home work question

OS: SLES 10 SP3 x864

Hypervisor: VMWare ESX or XEN

its a 2.6 GHz Quad Core Xeon machine (total 8 cores)

16 GB physical Memory

we are planning to run 10 to 12 Virtual Machines(each machine will use
1 GB Memory).

I have only 8 cores(two Quad Core processors)

1 - So can I run 12 virtual machine on this machine ?
2 - how many Virtual Processors I can assign to these Virtual Machines ?
(if I assign 2 Virtual CPUs to each VM then I need 20 physical cores
for VMs only - true ? )
3 - is there any best practice or method/rule for it .... I mean how
many(max limit) virtual machines could be run on a 8 core machines
without performance penalty ?

Steven E. Protter
Exalted Contributor

Re: maximum no of VMs on 8 Core machine - Best Practice


1. Maybe. Depends on how much memory. In this scenario I would say yes this will work.

2. Depends on which vmware implementation you use. With hyperthreading enabled 8 cores is really 16 cores to the OS and that provides you enough flexibility to get this job done.

3. No. Depends on the application. If you have a single server that is being pushed very hard, it will slow everything down. If one of your vm machines is Windows, the graphics overhead will drag you down. You need to carefully plan for what runs where and how much capacity you want in reserve.

The biggest problem with this setup will not be memory. You are only allocating 12 GB of the 16 GB to machines. The problem you might face will be I/O to and from disk. That is what must be carefully managed.

Steven E Protter
Owner of ISN Corporation
Sponsor: http://hpux.ws
Twitter: http://twitter.com/hpuxlinux
Founder http://newdatacloud.com
Trusted Contributor

Re: maximum no of VMs on 8 Core machine - Best Practice

You can easily run more than 12 VMs on this box.

If you are going to test for production, then you should be seriously thinking of installing OpenVZ on this machine. Xen/VMware can scale up with a large number of VMs on this box, the question would then be, what apps are you going to run from these.
The OpenVZ Wiki has an excellent write-up here, which looks like a relevant read for you


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Jimmy Vance

Re: maximum no of VMs on 8 Core machine - Best Practice

The generic answer I've seen elsewhare is basically 6 - 8 VM's per core and 8 - 10 VM's per NIC

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