Summary: Gregg O’Brien, Microsoft Premier Field Engineer from Canada, faces a problem with some Hyper-V guests, and troubleshoots it. Spoiler: He fixes it.

Recently I was working in my lab to test a configuration I was working on with a customer. I opened the Hyper-V Management Console and started a series of virtual machines. The virtual machines quickly counted up to 10% started, and then something strange happened: a number of them - but not all - froze at 10%.

I waited… and waited… and waited… but the VMs would not start. Being a seasoned IT professional, I treated this problem with the technical equivalent to antibiotics – I rebooted the server. Once again, I tried to start the VMs and again they froze at 10%. Like before, not all of the VMs, just a few. Others ran fine. Machines that did not start properly looked like this:

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After a slight meltdown and “softly whispering nice words” to the server, I opened up Bing and took a quick cruise around the internet to see if anyone had the same problem. Or better yet, if anyone had a solution. Turns out, people do run into this problem, but there weren’t any clear solutions. At least none that helped me.

I decided it was time to actually do some work and troubleshoot the issue. I opened up Event Viewer. Within the event viewer of Windows Server 2008 and Windows Server 2012, a log named “Hyper-V-Worker” will be generated on Hyper-V hosts.
Upon looking in that log, I found the following error:

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“'G-NAP1' Microsoft Emulated IDE Controller (Instance ID {83F8638B-8DCA-4152-9EDA-2CA8B33039B4}): Failed to Power on with Error 'The specified network name is no longer available.'

(0x80070040). (Virtual machine ID 58B2F029-5F6C-4147-AD8E-9ECCBD4A8EEF)”

With this message, I had two key pieces of information:
1) Something was wrong with an attached virtual disk device
2) It seemed to be network related.

I took a look at the properties of one of the affected VMs and found that it had an ISO file mounted. I forgot to unmount the ISO after installing the OS… I unmounted the ISO and restarted the VM, which then started up without issue.

But why would having a mounted ISO file prevent a VM from starting? Well, this whole scenario led me to find that my NAS appliance which hosted the ISO images decided to go on strike.

Hopefully not something you will ever have to deal with, but as a series of general rules to live by:

1) Failure of a network resource that hosts Hyper-V components may prevent virtual machines from starting

2) Always remember to unmount ISO files from VMs when finished with them

3) The Hyper-V-Worker log in Event Viewer is handy for all kinds of information regarding the operational status and health of Hyper-V. When in doubt, check this log!


Posted by Tristan Kington, MSPFE Editor, who was considering writing the intro as “the only PFE in Canada,” but thought it might’ve been taken seriously by the lunatic fringe. You know who you are.