VHD File

VHD stands for Virtual Hard Disk, a very common virtual drive file format mostly used by Oracle VM VirtualBox and Microsoft Windows Virtual PC (commonly termed as Hyper-V). These files are virtual but just act as a physical HDD to Hypervisors which in turn contain files and folders, its own file system and disk partitions.

A Virtual Hard Disk is alone an isolated hard disk giving users mobility to run multiple operating systems simultaneously on one computer.

VHD types

Based on their allocation pattern there are mainly 4 different types of VHDs

  • Fixed Virtual Hard Disk: A file combination of a raw disk image together with a footer and allocates size of a predefined disc.
  • Dynamic Virtual Hard Disk: An expandable file, that occupies the size of physical data present in it together with size of header and footer.
  • Differencing Virtual Hard Disk: A file consists of parent and child blocks, the parent consists of all the .vhd data and the child stores the changes done in vhd (parent vhd) thus providing the concept of undo. If required the child and parent can be merged.
  • Linked to a hard disk: a file which is interlinked to a physical hard drive.

Advantages of VHD file

  • Easy to deploy: VHD files can be copied and distributed over other virtual machines as per requirement.
  • Backup-and-Restore: just like other files, .vhd files can be backedup and can be restored in case of emergency.
  • Multi-User Isolation

Comparison between VHD vs. VHDx file formats

VHDX file format defined

VHDX is a virtual machine disk file format created with Microsoft Hyper-V (Windows Server Virtualization tool), supported on Windows 8, Windows Server 2012 and 2012 R2.

Comparison

  • Vhdx supports up to 64TB unlike VHDs which are limited to 2TBs
  • A virtual machine disk file captures the instance of a virtual machine state and stores that information as a file, with the upgrade in size of these virtual machine disk files from 64TB to 2TB, allows virtual disks to capture a detailed version of the instance of operating system.

  • VHDX use a 4kb block size unlike VHDs which uses a 512 byte block size
  • The change in block size from 512 byte to 4kb makes it in coordination with today's storage devices and suitable to format NTFS partitions.

  • VHDX are more prominent towards corruption regarding power failures unlike VHDs
  • VHDX keeps and regularly updates the changes in metadata periodically making it possible to fight against the corruption situations regarding power failures.

  • VHDX files can be resized live unlike VHDs
  • VHDX are only supported on Windows 8, Windows Server 2012 and 2012 R2.

Supported Hypervisors For Windows

Windows Microsoft Windows Virtual PC Microsoft Virtual Server Oracle VM VirtualBox VMware Workstation 11

Supported Hypervisors For MAC

mac

 

Oracle VM VirtualBox VMware Fusion 7

Supported Hypervisors For Linux

Linux

 

Oracle VM VirtualBox VMware Workstation 11