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Hyper-V Virtual Hard Disk Format Overview

Published: February 29, 2012

Updated: November 1, 2013

Applies To: Windows Server 2012, Windows Server 2012 R2



As enterprise workloads for virtual environments grow in size and in performance demands, virtual hard disk (VHD) formats need to accommodate them. Hyper-V in Windows Server 2012 introduces a new version of the VHD format called VHDX, which is designed to handle current and future workloads.

VHDX has a much larger storage capacity than the older VHD format. It also provides data corruption protection during power failures and optimizes structural alignments of dynamic and differencing disks to prevent performance degradation on new, large-sector physical disks.

The new VHDX format in Windows Server 2012 addresses the technological demands of an evolving enterprise by increasing storage capacity, protecting data, and ensuring quality performance on large-sector disks.

The main new features of the VHDX format are:

  • Support for virtual hard disk storage capacity of up to 64 TB.

  • Protection against data corruption during power failures by logging updates to the VHDX metadata structures.

  • Improved alignment of the virtual hard disk format to work well on large sector disks.

The VHDX format also provides the following features:

  • Larger block sizes for dynamic and differencing disks, which allows these disks to attune to the needs of the workload.

  • A 4-KB logical sector virtual disk that allows for increased performance when used by applications and workloads that are designed for 4-KB sectors.

  • The ability to store custom metadata about the file that the user might want to record, such as operating system version or patches applied.

  • Efficiency in representing data (also known as “trim”), which results in smaller file size and allows the underlying physical storage device to reclaim unused space. (Trim requires physical disks directly attached to a virtual machine or SCSI disks, and trim-compatible hardware.)

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