Normally, you can calculate the average number of VMs depends on the
computing power (CPU). For example, 1 physical core can supports 2 VMs with
2 GB RAM. If you have 2 CPUs with 16 cores, then you might run 32VMs with
64GB RAM. However,  the max number of VMs per host depends on variable
facts as Al Quiros mentioned, In addition to Al's comments, you might also
consider the application you want to run on guest VMs. If applications are
more computation intensive, the number of CPUs would be important fact to
decide the max number of VMs per host.

 In our environment, we don't use VMware but running  RHEL 6 x64 with KVM
on IBM blade hosts with 16 CPUs and 24GB RAM. We run average 15 Windows XP
VMs with 1GB memory without much performance overhead. However, we can run
up to 22 VMs  but the performance was not good.

Best regards,
Young Hyun Oh
IBM Tivoli

From:   Evelio Quiros <>
To:     ""
Date:   05/24/2012 10:58 AM
Subject:        Re: Max Number of VMs per Host


As you know, the number of Virtual Machines per host depends on available
resources (CPU, RAM, Disk), as well as the demands of the image.
As a general guide, I have found the following to be reasonable. Other
admins, please share your opinions.

For a single VM host with 12 virtual CPU and 98 GB RAM, I typically
allocate 25 Windows VM. When necessary, I have raised it to 32 Windows XP
machines. For linux based images, I have used 50 VM without issues. Monitor
the performance tab on your vSphere client to see if the host is
On Virtual Machines that require higher performance, I usually will not
place them on a host with more than 10 working VM. But the most important
thing is to watch the performance closely. You will get a feel for how many
VM per host by experience.
As always, your mileage may vary.

Al Quiros
Florida International University

From: <Sanders>, Arbin D <>
Reply-To: "" <>
Date: Wednesday, May 23, 2012 3:53 PM
To: "''" <>, "
''" <>
Subject: Max Number of VMs per Host


What is the number of VMs do you all run per VMware host? Is it limited to
the RAM limitation for vSphere 5? How many purchase vSphere licenses?

Arbin Darren Sanders

IT Manager – Academic Computing
North Carolina Central University
712 Cecil Street
Suite 3014
Durham, NC 27707
919.530.5097 (Fax)

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