Hyper-V Virtual Machines Not starting, Read-Only Disk

Friday, February 27, 2009
by asalvo

I went to RDP into one of my local Hyper-V virtual machines this morning, only to find out I wasn’t able to connect. Browsing to the Hyper-V manager I saw that none of my VM’s were running. At first I couldn’t figure out why this was, until I remembered that my desktop machine was powered off this morning, indicating we had a brief power outage. The laptop, which obviously has a battery, was able to withstand the power outage, but the external hard drive, which requires external power was not. While I do have a UPS, it’s a piece of crap that never worked. Maybe now would be a good time to pick up another UPS on closeout from Circuit City, I’ll have to run that one past my manager.

I tried starting my VM’s, but most of them wouldn’t start, giving an error stating that the VM couldn’t start in it’s current state (which appeared to be saved). I tried to delete the saved state, and got an error stating that the saved state could not be deleted in the current state. The common thing between the VM’s that would start, and those that wouldn’t, was that the VM config files were also on the external hard drive. Browsing to the external hard drive, showed that the folder that contained the VM config files was empty (not a good sign). I checked the event log to see if I could get some more information, and 100’s of warnings indicating a problem with my external hard drive. I figured the best thing to do at this point was to shut down my laptop, power cycle the external hard drive and double check all connections.

After the reboot, the drive was functional (well almost) again, and there were no more warnings in the event log. While the VM config files were back where they were supposed to be, I still couldn’t start the VM’s. I also could not delete the VM config files from within Hyper-V manager. I went back to the config folder and went to Cut/Paste (move) the config files someplace else thinking I would just recreate the VM config. However, I couldn’t cut, move, delete or do anything other then browse (read) the files and folders.

Jumping back to Server Manager, I opened up Disk Management utility and saw that my external hard drive was listed as read only. I looked in just about every place I could think of, but could not find a way to make the disk read/write again. A Google search yielded no usable results, as it seems this is a pretty obscure problem. Aside from the legitimate answer of “does your removable media have a write protect switch”, all the other answers seemed to focus around viruses and other seemingly unrelated solutions.

Finally I decided to try my the only option that wasn’t grayed out for the read only disk in Disk Manger, and that was to take the disk offline, then bring it online again. Wow, that fixed it, the disk was now back in the standard read/write mode, and finally my VM’s would start. It appears as if the VM config file on at least one of the VM’s was corrupted, as I had to reselect my network adapters, but that was an easy fix.


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