How many Server 2012 R2 virtual servers can be installed in Hyper-V?

ditobot used Ask the Experts™
I am considering using a beefed up IBM server with two 8 core Xeon processors and 64GB or RAM to create a private cloud in our office. I am new to virtualization and I'm trying to wrap my brain around best practices and methodology behind creating said private cloud.

Originally I was thinking of installing three virtual servers on this machine. A DC, Exchange 2013 and an Exchange 2013 front end server. I already have a standalone primary DC but I'd like to put a backup DC on this machine.

I believe that there is a two instance limitation on Hyper-V but I'm not sure how the virtual servers are rolled out to those instances and what the limitations are. I've setup virtual Linux servers in Amazon's AWS environment and it's always been a machine per instance.

Am I barking up the wrong to to accomplish what I am trying to accomplish? Should I be looking at VMware instead or is this possible in Hyper-V?

Sorry for the potential vagueness of my question but I am having a hard time finding a starting point.

Thanks in advance.
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Neil RussellTechnical Development Lead

You can install as many as you have a license for.  The TWO limit is for a single license of Windows 2012 STANDARD.  And that is one licence PER 2 Physical CPUS in EACH Physical Server.

If you want to run 4 VM's then if your host has 1 or 2 CPUs you need two windows 2012 Standard licenses.  once you go to large numbers of VM's you will need to look at Data Centre Licenses.
Rob GMicrosoft Systems Engineer
It's not a question as to if it will work, it will, but the issues you will have will happen in both VMware and in Hyper-V. Depending on the size of the environment you will kill the disks on the server due to I/O of Exchange. You will need a substantial server to handle this.. Or will need to break it up into two servers.. While VmWare IMO is better, it is WAY more expensive... So for a cost comparison, i would suggest HyperV.

With that in mind..
I have 4 machines running on two different 2k12 Hyper-V servers (4 on each) (soon to be 4 on one and 3 on another)
The servers were 17K each.. Keep that in mind...
Both are dual12 core Xenon processors
have 512GB DDR3 1866mhz
Have a raid6 setup with 4TB 15k sas drives
and have 6 NIC connections connected to a cat6 gigabit network..

Even with this, one of the servers that runs our exchange is a turd as far as performance and i have been looking to move it back to physical..  It's just the Disk I/O is ridiculous.. and i only have 75 mailboxes to deal with.. If it was 100, it would crash, i am sure of it..
Microsoft best practice is to keep Exchange physical.. While it does work Virtual, i would suggest against it..
Technology and Business Process Advisor
Most Valuable Expert 2013
Hyper-V has no realistic limit to the number of machines you can run.  The "limit" is in how many VM Licenses are included with a copy of Windows Server you purchase.  Data Center licenses have no limit.  Standard licenses come with 2 licenses that can only be installed in virtual machines (on Hyper-V or anything else) or ONE physical license (there is also 1+2 licenses which means you can install a GUI version of Windows, add the Hyper-V role and any feature to manage it but NOTHING ELSE.  You cannot use the physical install as a DC, a file server, a print server, a database server, etc.  ONLY Hyper-V and Hyper-V management.  THEN you can still use the two Windows VM Licenses.
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Lee W, MVPTechnology and Business Process Advisor
Most Valuable Expert 2013

You might also want to check out resources on Virtualizing Exchange.

I disagree with Rob G. - I used to work with an organization that has 3 exchange servers for 1000+ people, all running in VMs.
Neil RussellTechnical Development Lead

Poorly configured systems are not a reason to avoid virtualisation.  We have 4 exchange servers, 2 DB and 2 WFE, all virtualized and all running perfectly.  These handle in excess of 4,000 mailboxes and uptime is as long as it wants between patching.
Running 100 mailboxes on an exchange server should just about warm it up, Disk IO on a server with 100 mailboxes should not be a problem unless your mailboxes are all used for a few 1,000 emails a day per user.
Rob GMicrosoft Systems Engineer

What was the VM?
VM or virtual machine doesn't really help tell what the specs were..
I too worked for a company that ran VM's on Cray servers, which didn't have the same issue with a Microsoft exchange cluster a few years ago.. but those servers start at 130K... A little different then a typical dell....

Which at 40 Petaflops i am sure it wouldn't have the latency issues..
Lee W, MVPTechnology and Business Process Advisor
Most Valuable Expert 2013

I'll have to get back to you on the config and check with them.  I'm fairly certain they've upgraded since.  But I'm also fairly certain it wasn't a cray.  Honestly I would question disk and RAM config if you were having problems with Exchange for 75 users.
Rob GMicrosoft Systems Engineer

They get around 800 emails "Per user" daily, plus due to compliance they require journaling to be enabled.
In addition to that there are email attachments on 90% of the emails... And for compliance i need to store all the PST files on the Exchange server, they are quota'd on the mailbox, but attached in 3GB increments every 3 months.. Roughly 1-2GB per month per user.. It's not easy.. Especially with one exchange server.

the other Vm's on the system are..
Print server
and two database servers, but they are low consumption servers.. DB size is about 100mb on each, and doesn't grow much..
Neil RussellTechnical Development Lead

PST files???
Why do you have PST files with an exchange server?
Why do you have exchange databases on a RAID 6 configuration?

Like I said, a poor config is not an excuse to blame virtualization.

If your servers cost you 17K each then you should have a decent storage array that has correctly configured raid arrays for the systems in use.  Exchange databases should be on Raid 10 for performance, system and logs can be raid 5/6 if cost is the issue.
Neil RussellTechnical Development Lead

Hyper-v is as good a choice as any and in your case the cost is considerably less for Hyper-V.

I'm sure what you are meaning with instances?

You will have a host server set up with 3 VM's running on it.  Where do instances come into it?

Sorry if i misunderstand.


I read somewhere that there was a two instance limit, but I think based on the conversation it is per Standard 2012 R2 license. The verbiage was tripping me up in the Microsoft licensing information.

One last question since we've rattled some cages on best practices and configurations. Everything I've read points to RAID 10 as the preferred method for the arrays. What is the preferred method to partition the drives for the VMs. I read somewhere that Hyper-V installation and the VM database should be on separate partitions. What suggestions do you guys have for partitioning the array for maximum performance and security.

Neil RussellTechnical Development Lead
That is correct.  In an ideal world you would have a raid 1 array of 2 disks for the Hyper-v OS install and then additional arrays for your VM's and data disks.  As you correctly state, raid 10 is the microsoft recommended raid config for the database and logs if possible but at the very minimum for the databases. The OS and logs can sit on raid 5 or 6 arrays without too much degradation in performance.
If you search google for Microsoft best practice for exchange virtualization you will find many Technet and MSDN guides and videos that will explain how best to avoid bottlenecks and poor IO.
Andrew Hancock (VMware vExpert / EE Fellow)VMware and Virtualization Consultant
Fellow 2018
Expert of the Year 2017

Both VMware vSphere and Microsoft Hyper-V  perform the same, and are very good enterprise Hypervisors.

Licenses aside, you can create as many virtual machines (instances) as resources dictate, e.g. CPU and Memory, memory normally being the bottleneck.

e.g. you will run out of memory, before CPU and storage.

Depending upon the utilisation of your virtual servers, we usually scale 5-6 VMs per physical core.

So we've had 40 virtual machines running on a

two 8 core Xeon processors and 64GB or RAM .
VB ITSSpecialist Consultant
Top Expert 2014

@ditobot, have a read of this article for a very good explanation of how 2012 R2 licensing works with 2012 R2 and Hyper-V VMs in various scenarios. This helped me out greatly when 2012 R2 first came out and we wanted to spin up some 2012 R2 VMs for testing.

As for RAID arrays, I usually configure a RAID1 array for the Hyper-V host installation and then a RAID10 array for the VMs, along with a single non-RAID disk for non-essential stuff like dedicated VHDs for pagefiles, VSS data, etc.

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