What is Virtual Hard Disk

Technology Overview, November 13, 2017

vhd drive

VHD or the Virtual hard disk created with Microsoft Hyper-V, Virtual PC, Virtualbox is basically a disk image sort of file format that is used to store the complete data of a hard disk. Hyper-V in the Microsoft Windows Server 2012 has also introduced a new VHD format version called the “VHDX” that is specifically designed for handling the current as well as increasing data storage support in the future.

Prime Advantages of the New VHDX File Format

VHDX format in MS Windows Server very nicely addresses most of the technical demands of any evolving organization by 1) augmenting the storage capacity, 2) salvaging the data against corruption, and 3) improving performance over big-sector disks.

VHDX File format – Technical Overview

  • Supports virtual hard drive capacity for data storage as large as 64 TB.
  • Protects well against data loss and data corruption in the event of power failure as it logs updates to the metadata structures of VHDX.
  • Improves virtual hard drive format alignment so as to work nicely over big sector disks.

VHDX Format Features

  • Bigger sizes of the blocks for differencing & dynamic disks, helping them for attuning to the workload requirements.
  • The 4-KB logical sector virtual drive is allowing for better and augmented performance while using it by the applications and for the workloads, which are designed for the 4-KB sectors.
  • It stores the custom metadata for the file which the end-user may wishes to record, like, the OS version or the applied patches.
  • Better efficiency in the representation of the data (which is also called as “trim”). This results in lesser file size and also helps the principal physical storage device to retrieve the unused space.

VHD vs. VHDX

  • Storage Capacity:
    A great advantage of the VHDX format is its much bigger virtual storage capacity than the previous VHD format. Before the release of the MS Windows Server 2012, the Hyper-V virtual hard drive only had 2 TB storage limit; whereas, the VHDX files can store up to 64 TB of data.
  • Performance:
    The advantage of the VHDX format is not just limited to the augmented data storage capacity, but also, the VHDX files are designed to easily work under today’s conditions with the modern day hardware along with having a 4 KB logical sector size which helps in improving the performance as compared to the older VHD files.
  • Data Corruption:
    The new VHDX files provide ample protection safeguarding the data against corruptions in case of power failures. This is done by constantly keeping a track of the metadata updates, which is a feature that was not there in the VHD format.

The Hyper-V VHD or the New VHDX?

Let us look at some of the advantages, disadvantages, and limitations

VHD Features VHDX Features
For moving the disks around several host versions of MS Windows, VHD is the best bet. Microsoft has improved the VHD format, which is now VHDX with a multitude of improvements and advancements that were added to it, so as to better race with the VMware.
Internally, it utilizes a 512-byte size of the block.
The block size of 4KB aligns it very well with the modern day hard disks also allowing the use of 4KB internally.
Limited to just 2TB. Disk size as large as 64TB supported.
One cannot resize the VHD live. Live resizing of the virtual disks is possible.
Lower efficiency in handing conditions such as power failure. Better handling of situations such as power failure.
VHD works well on MS Windows Server 2012 R2, 2012, 2008 R2, and 2008. The Hyper-V on Microsoft Windows 8 versions even supports it along with supporting the Virtual machines as well as the Server. VHDX is supported only on the MS Windows 8 version and the Microsoft Windows Server 2012 version and the versions later than these.
Handling of snapshots. Better snapshots handling.

 

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