Hyper-V

Hyper-V 2019 will NOT mount ISO from a network share.

Like most IT guys. They have a repository of their ISO images saved on a network share so that they can mount the ISO if needed on multiple machines. I recently switched to Hyper-V and have been having an issue with creating VMs and using my ISO from my network share to do so.
Hyper-V Manager available through RSAT doesn’t have an option to mount an ISO or capture a drive from a machine on which is running. Instead it gives you drives of the Hyper-V host, and that would of course require you to have an ISO or the disc itself present on the host. I didn’t want to do that. I would rather have my repository share available for that purpose to allow for all the drive space to be available on the Hyper-V host.

So, I would map a network drive with my ISOs. The mapping would succeed, but mapped drive (letter) will not be visible in Hyper-V manager when trying to mount an ISO. Okay, so next I tried mounting from UNC share directly, but that would also fail, with the message:
“‘VM’ failed to add device ‘Virtual CD/DVD Disk’” “User account does not have permission required to open attachment”.

hyperv1
Access Denied Error when trying to mount the ISO

It goes back to the constrained delegation requirement for the Hyper-V host accounts to be used to perform functions such as this. This has been a pain to say in the least, as I have also had issues with live migration with my machines not being clustered due to different hardware.

So, in researching, I found this blog post. It has helped me through this issue with mapping the shared folder with the ISOs.

The cause of the problem is that the Hyper-V is intended to run with VMM Library Server and to mount files from it, not any random share. To re-mediate this:

  • You need to assign full NTFS and share permissions to computer account of Hyper-V on a shared folder with ISO’s you want to mount.
  • In AD on the computer account of Hyper-V machine delegate specific service ‘cifs’ to the machine you want your ISO’s mounted from. Microsoft calls this constrained delegation.

Here is step by step procedure for the constrained delegation:

  1. Go to Active Directory Users and Computers
  2. Find the Hyper-V server computer account and open up its properties.
  3. Go to Delegation tab.
  4. Select Trust this computer for delegation to the specified services only radio button.
  5. Click the Add button.
  6. Click the Users or Computers… button.
  7. In the Add Services window, click Users or Computers and enter the computer account that will  act as a library server and click OK.
  8. Select the cifs Service Type and click OK.

The resulting setup should look something like this:

Constrained delegation
What the configuration should look like for constrained delegation

I added both the server that contained the ISO images and the server that I run my RSAT tools from just to be safe. I next rebooted the Hyper-V host (that is a requirement).
When the host rebooted, I was able to successfully create the VM.

Hopefully, this will also solve my issue with live migration between my hosts. I will have to test that again and will inform everyone here if that succeeds as well!

PLEASE COMMENT!
THANKS FOR READING!

References:
Hyper-V Server 2012 won’t mount ISO from a network share
Hyper-V authentication in Windows Server 2016 for managing remote Hyper-V servers through RSAT
Constrained Delegation

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