Hyper-V: Ensure sufficient physical disk space is available when virtual machines use dynamically expanding virtual hard disks

This article is intended to provide more information about a specific issue that can be identified by running a Best Practices Analyzer scan for Hyper-V. It also can be used without running a scan, as general troubleshooting and best practice information to help you configure your server appropriately. If you have troubleshooting steps or information that would improve this article, please add it. For instructions on how to edit a TechNet Wiki article, see Wiki: How to Use the Editor.

For more information about best practices and scans, see Run Best Practices Analyzer Scans and Manage Scan Results.

Note: The following sections provide details about the specific issue. Italics indicates UI text that appears in the Best Practices Analyzer tool for the specific issue.

Issue

One or more virtual machines are using dynamically expanding virtual hard disks.

Impact

Dynamically expanding virtual hard disks require available space on the hosting volume so that space can be allocated when writes to the virtual hard disks occur. If available space is exhausted, any virtual machine that relies on the physical storage could be affected. This impacts the following virtual machines: <list of virtual machines>

Resolution

Monitor available disk space to ensure sufficient space is available for expansion. Consider shutting down the virtual machine and use the Edit Disk Wizard in Hyper-V Manager to convert each dynamically expanding virtual hard disk for this virtual machine to a fixed sized virtual hard disk.

Additional references