I had an IT consulting customer email me requesting assistance with extending the system partition on a Windows 2003 virtual machine. The partition had been running low on disk space for a while. The customer had extended the vmdk using VMware, but was unable to extend the partition using diskpart. This is normal behavior for a Windows 2003 system so I scheduled downtime so that I could use VMware Converter to fix the problem.

I have done this operation a number to times in the past. You simply tell Converter to convert the VM and target the same ESX cluster with the imported copy. During the operation, VMware gives you the option to change the partition size. Windows recognizes the partition size change at first boot and you are good to go. However, the customer failed to tell me that they had un-marked the c:\ drive partition as active while trying to get the disk to extend. When I shut the VM down to clone it, it never came back up. Neither did the imported copy. Both were completely useless. They would boot to an “Operating System not found” error. [more]

I tried fixboot and fixmbr from the recovery console but neither worked. I ended up restoring from a CommVault backup. Later, based on some comments from coworkers, I decided to see if I could fix this problem by mounting the disk to another VM and adding back the “active partition” status. I mounted the vmdk that was broken to a Windows 2008 server and using disk manager re-marked the partition as active. Sure enough, after dismounting from the temp VM the original VM booted up no problem. Just one more reason to use virtual machines.