How To Enable Shared ISOs in Hyper-V

I'm wrapping up my TrainSignal course (shameless plug) on Microsoft Exam 70-247: Configuring and Deploying a Microsoft Private Cloud with System Center 2012 and I've come across a few tips that I thought would be useful. Let's start off with a useful how-to around ISOs.

When you create a VM, the default behavior of an ISO attached as a virtual CD/DVD is to copy that ISO into the VM's directory. This is Microsoft's way of avoiding Live Migration failures when you try to move a VM with an attached virtual CD/DVD from host to host. As you should be aware, in both Hyper-V and ESX/ESXi an attached ISO would prevent a vMotion or a Live Migration.

Personally, I prefer that the VM fail the migration -- it would then force me to change my configuration rather than implement this overly over-thought and very space-inefficient method. Luckily, Microsoft has provided a work-around that is much better: Why copy the ISO image? Instead, share the ISO image from the VMM library, end of story. Of course, I wish it was that simple. The checkbox in Fig. 1 enables the sharing of the ISO image (as opposed to copying it), but you still have to perform some added steps in the background to make it work:

1. Grant the VMM Service Account Read access on the share that is hosting the ISO image in the library.
2. Grant each one of your Hyper-V hosts Machine Account read access to the shared location of the ISO.

Figure 1. In Hyper-V, enable sharing of the ISO and then perform the extra steps. (Click image to view larger version.)

Once you complete the two steps, you have to configure constrained delegation. You can do this from any computer that has the Active Directory Users and Computers console or from a Domain Controller.

Constrained delegation basically instructs every Hyper-V host's machine account to present delegated credentials for the CIFS/SMB protocol to the VMM server where the library hosting the ISO file resides. You will have to perform these steps on each Hyper-V host's machine account in AD separately:

1. Open Active Directory Users and Computers.
2. Locate the Hyper-V host machine account, right-click and go to Properties.
3. Select the Delegation tab and click Select this computer for delegation to specified services only.
4. Click Use any authentication protocol.
5. Click Add.
6. Add the VMM Library servers that contain the ISO you want to share and click OK.
7. In the Available Services list, click cifs (see Fig. 2) and click Add.

Figure 2. In the Available Services list, click cifs and click Add. (Click image to view larger version.)

This should now allow you to share the ISO image each time you attach it. This will also allow you to have successful Live Migrations while a CD/DVD virtual drive is attached.

Posted by Elias Khnaser on 01/09/2013 at 2:57 PM