In this post I’ll show how to resolve the issue of a VM that’s stuck in the “backing up…” state as shown by Hyper-V Manager, without having to reboot the virtual host.
If a VM is stuck in the backing up… state it’s probably due to an error with the Microsoft Hyper-V VSS Writer. Open an elevated command prompt and run “vssadmin list writers”. The output should look like it does below, with no errors listed.
The Microsoft Hyper-V VSS Writer runs within the Hyper-V Virtual Machine Management service, so in order to restart the VSS writer and clear the error, you have to restart the Hyper-V Virtual Machine Management service. I’ve restarted this service without any issues, but please test this on a test server first.
You can restart the service from the Services mmc, but if the Hyper-V VSS Writer is in an error state the service may hang on shutdown, in this case you’ll have to kill the vmms.exe process from Task Manager.
When you do this VMs will disappear from Hyper-V Manager, but will reappear when you restart the Hyper-V Virtual Machine Management service. Following the service restart the VM should no longer by in a backing up… state.
Richard Skinner 
Worked a treat. Great knowledge to have.
Hello !! I found your great article through google . Do you know if there is a downtime for the virtual machines running on the host if i kill the vmms service ?
Thanks
In my use of this method there’s been no downtime, but please verify on your test environment first.
Thanks a lot Richard. I will try it !
Man your article saved my day. within minutes I was able to get my VM running back again, thank you very much for sparing so much of your time to post everything in detail
Did you test restarting the Hyper-V Virtual Machine Management service in a Cluster? Will the VMs try to fail over when the service is restarted?
Yes I’ve done this on a cluster and the VMs don’t fail over. When you restart the service the VMs disappear from Hyper-V Manager on the node where you restart the service. When the service has re-started they reappear.
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I never saw what you saw in the command prompt. Mine Says, after the intro text:
“Waiting for responses.
These may be delayed if a shadow copy is being prepared.”
Trying to kill the vmms process gets it stuck “Stopping”. Killing the process and restarting it in Task Manager doesn’t work, the mmc plugin fails to load.
I just had the issue this morning. Windows Server 2012.
I even tried using taskkill running as Administrator. It will not let you stop the vmms.exe process even after the command to stop the service times out.
Stopping the service just makes the MMC non functional, which is worse because now you don’t even know if the VMs have come out of the “Backing Up…” state.
Getting the same issue and then have to restart the host to get everything back… and still stuck in a backup state.
This is a rather annoying issue as it is preventing our backups from running
Thank you so much,
This article solved my problem with the Hyper-V
This works on one of my Hyper-v hosts, but on the other when I try to kill vmms.exe, I get “Access Denied.”
hi, does patching windows solve this issue?
It worked today (03/02/2017) on Hyper-V 2012 R2
Thank you! You saved my day!
Hi Richard, we’ve referred to your article now twice for one of our client environments, but because have our own working and verified backup in place, we don’t need the native Hyper-V backup service – how can we disable it permanently?
Thanks, worked great!
I had the same on a windows 2012 R2 server 1 vm server did not want to start after shutdown 4 other sessions were running in backup. nothing was in error. restarted the main server. everything went in to merging. that took 30 minutes and even the stopped sever was running again after the merge completed. backup files disapeard.
This was a real life saver. Thank you!
Hi ,
Your Solution work with me .
Thanks a lot
HI
saved my day today in Cluster-Environment.
We had to kill the vmms.exe in Taskmanager. Some Service-Guard starts the vmms.exe immedatly aber kill and the Hanging Machine starts merging.
Hi.
Thanks a lot, this article helped in my enviroment.
In my case, it was nececessary finished process vmms.exe and start the service.
Thanks a lot again.