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Hyper-V: VHD-format dynamic virtual hard disks are not recommended for virtual machines that run server workloads in a production environment

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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.

Operating System

Windows Server 2012

Product/Feature

Hyper-V

Severity

Category

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 use VHD-format dynamically expanding virtual hard disks.

Impact

VHD-format dynamic virtual hard disks could experience consistency issues if a power failure occurs. Consistency issues can happen if the physical disk performs an incomplete or incorrect update to a sector in a .vhd file that is being modified when a power failure occurs. This affects the following virtual machines: <list of virtual machines>

Resolution

Shut down the virtual machine and convert the VHD-format dynamic virtual hard disk to a VHDX-format virtual hard disk or to a fixed virtual hard disk. (The VHDX format has reliability mechanisms that help protect the disk from corruptions due to system power failures.) However, do not convert the virtual hard disk if it is likely to be attached to an earlier release of Windows at some point. Windows releases earlier than {1} do not support the VHDX format.

Additional references