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lasinl
Enthusiast
Enthusiast

how many VMs per CPU?

Is there a rule of thumb or formula for figuring out how many VMs you can run per CPU in a given host?

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NuggetGTR
VMware Employee
VMware Employee

really depends what type of workloads will be running, 25 vCPUs per core is the limit. but guess average is around 6 to 10 vCPUs per physical core.

________________________________________ Blog: http://virtualiseme.net.au VCDX #201 Author of Mastering vRealize Operations Manager
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MKguy
Virtuoso
Virtuoso

As so often, the only "correct" answer is "It depends".

It depends entirely on your workload characteristics and physical hardware. There is no easy rule of thumb that can be even remotely considered accurate.

Generally, light consolidation and "normal" VDI environments on modern CPUs should yield you something around 4-8 vCPUs per physical core. With Xeon CPUs with HT you can go beyond that too.

Some other CPU-intensive and real-time workloads might end up suffering from a host running more vCPUs than physically available cores/threads.

-- http://alpacapowered.wordpress.com
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sparrowangelste
Virtuoso
Virtuoso

if you are doing consolidation take your current cpu usage and estimate from that.

that is a rough estimate of course.

If noticed that the real bottleneck is ram not cpu normally.  you would probably cap your ram before you even max your cpu.

--------------------- Sparrowangelstechnology : Vmware lover http://sparrowangelstechnology.blogspot.com
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RR9
Enthusiast
Enthusiast

i think ..it depends .. one of the important factor would be capacity of the host, you can have as many below maximum limit. if you have hosts with 96GB RAM and 8 CPUs ... if you are having biggers VMs like 16 vcpus see how much that VM is going to consume ..for example if it consumes 90% then its not good as it can eat the much part of the hosts computing power. Then definitely consolidation ratio will be less.. another factors are what is the real target ..to achieve consolidation ratio or to virtualize the server etc..there are various documents available which you can refer for capacity planning..

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TomHowarth
Leadership
Leadership

This is one of the ultimate Consultant answers "it Depends"

it depends on what processor you are using, it depends on the operating system, it depends on the workload profile. there is no easy rule of thumb here.

Tom Howarth VCP / VCAP / vExpert
VMware Communities User Moderator
Blog: http://www.planetvm.net
Contributing author on VMware vSphere and Virtual Infrastructure Security: Securing ESX and the Virtual Environment
Contributing author on VCP VMware Certified Professional on VSphere 4 Study Guide: Exam VCP-410
vTagion
Enthusiast
Enthusiast

I have seen people that do a ratio of 1.5:1. I have seen others who will go up as high as 8-10 vCPU (or higher). For me, I honestly take the data of CPU utilization on the application servers I will be running in my new environment and build out from there. If this is your first time you could take things a little slower as you introduce them into the environment and see how the host handles the load and go from there. Worst case scenario is you add another host to your cluster/environment. You just want to be sure that your CPU Ready stats are very very low (or zero).

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lasinl
Enthusiast
Enthusiast

Okay, it sounds like 10 VMs per physical core is the agreed upon real world limit. I'll adopt that. Most of my VMs are LAMP servers (with 1 GB of memory) for various web and mobile apps I'm developing - they barely consume any processing power since no one is actively FTP'n/GIT'n/dev'n on them.

My current host is a SFF desktop with a Core 2 Duo E6600 2.4 GHz processor. But I just scored a tower with a XEON E5520 Quad Core 2.26 GHz proceesor, so this will replace my current host. Since it will be a host with the more powerful XEON processor, what would you guestimate as to how many VMs/vCPUs I may be able to get out of each core?

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