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How to check file system alignment of Dynamic Disks in Windows Virtual Machines

Last Updated:

Applies to

Windows virtual Machines


The mbrscan or any other Windows utilities commonly used to check for misaligned I/O, including msinfo32, diskpart and wmic, will not reliably report the starting partition offsets of Windows Dynamic Disks.

The only way to accurately assess the alignment of Windows Dynamic Disks is by using the Windows Support tool dmdiag.exe. The tool is available as part of the Windows Server 2003 Support Tools. For an updated version, see

Additional information on using dmdiag can be found in the Microsoft TechNet article - Disk Partition Alignment Best Practices for SQL Server


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