Hyper-V Guest OS newer than Host OS

Our domain has a server running Windows Server 2008 Standard.  I need to create a Virtual Machine on this box that will be running Windows Server 2008 Standard R2.

I would ordinarily update the Host OS, but this server is being accessed for data from over 100 end users.  I cannot shut down the server; hence, the need to create a VM while the Host machine is still being accessed by those end users.

Is there a problem with having a newer Guest OS than the Host OS?
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JohnBusiness Consultant (Owner)Commented:
I am not certain about Hyper-V, but for VMware, it is absolutely possible to use a newer guest than host. I have done that.  Hyper-V should work because the guest is just a machine.

.... Thinkpads_User
Cliff GaliherCommented:
There are indeed problems because of how Hyper-V handles device drivers and integration. Updating the host OS is really no different than any other maintenance task that requires interruption. Most OS and product patches require that various services be taken offline during the entire patch installation, and also require a reboot. How do you handle those? For services that truly need high availability, they are often deployed in farms or clusters so that an individual member can be taken offline and upgraded. This addresses almost all situations, patching, upgrades, unplanned failures, where the tolerance for interruption is very low. Hyper-V fully supports clustering and live migrations.
baleman2Author Commented:
To cgaliher:

Doesn't a move from "Standard" to "Standard R2" mean that the server is wiped clean and the OS is installed as though on a new server.  Installation of "R2" isn't the same as installing Windows updates, is it?
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JohnBusiness Consultant (Owner)Commented:
Any Windows host requires maintenance and occasional restart (meaning guest systems have to be shut down). This is the same for VMware Workstation and Server and is independent of guest.

If you want a host that stays up, then consider an VMware ESX host. That will be a better choice if the guests cannot be shutdown except rarely.

... Thinkpads_User
Cliff GaliherCommented:
The OS does indeed need to be wiped clean to go from 2008 to 2008 R2.

But hyper-v should NEVER be run alongside other roles. So enabling hyper-v on a machine where clients are accessing data would be very bad.

If this data resides in a VM and hyper-v already is on, just move the VM to a new machine for the duration of the host upgrade.

Regardless, hyper-v should run alone, and the guest should always be the same version or older; never newer.

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baleman2Author Commented:
I don't want a Host that has to stay up indefinitely.  I understand the need for updating the Host which means shutting down the VM while updates are installed.

I want this box to stay up and running while I create a VM on it - while simultaneously satisfying (no latency) the requests of 100 domain users.  The VM must have 2008 Server R2 on it while the box just has 2008 Standard (no R2).

After the VM has been created, I intend to allocate 90 percent of the box's resources (hard drive space and Ram memory) to the newly created VM.  The 100 domain users would then begin to access the VM instead of the software on the box itself.
Cliff GaliherCommented:
Well, as I said, you'll have issues running 2008 R2 as a guest on a 2008 (non r2) host. So while that probably sounded like a great plan, you'll want to go back to the drawing board and come up with a new upgrade strategy.
JohnBusiness Consultant (Owner)Commented:
You can consider VMware Server, but performance will not be as good as VMware ESX or Hyper-V.

With VMware ESX you can run any server on the guest compatibility list.  This is true for VMware Server as well.

... Thinkpads_User
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