Virtual hard disk format

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Virtual hard disk
File extension : .vhd, .vhdx
Developed by: Microsoft (originally: Connectix )
Type: Container file
Container for: any files
Contained in: Virtual PC ,
Virtual Server ,
Windows 7 etc. v. m.
Website : technet.microsoft.com/de-de/library/dd440864(WS.10).aspx

The VHD (short VHD format , in English Virtual Hard Disk for virtual disk ) is a container - file format and has the usually file extension .vhd . It was originally developed by Connectix for the Virtual PC and Virtual Server , since its takeover by Microsoft and supported directly in the operating system from Windows 7 onwards.

Technical details

Virtual disks in the VHD format can from 7 Windows on the contained therein disk management and with the command-line tool DiskPart be created with either a fixed or a dynamically growing size. The maximum size for dynamic and differential VHDs is 2  tebibytes (around 2.2  terabytes ), the maximum size of VHDs of fixed length is not limited per se, but in practice by the maximum file size of 16 tebibytes (around 17.6 terabytes) per file (with NTFS ) limited. In the case of dynamic size, only the maximum size is specified during creation, which the container file must not exceed. With the fixed size, the file is exactly the same size as it was specified when it was created - regardless of whether it is actually filled with data or not.

With Windows 8 and Windows Server 2012 , the file format was expanded as “VHDX” and can now handle hard disk images with a maximum size of up to 64 Tebibytes (around 70 Terabytes). The Explorer has also been expanded accordingly so that such memory images can be accessed directly .

The biggest disadvantage is that a dynamically growing or differential hard disk cannot be expanded or reduced in retrospect (with Windows on-board tools). Only a hard disk with a fixed size can be expanded later. However, external tools (such as the VHD Resizer ) are available for this. In addition, the data can also be copied manually to larger or smaller (virtual) hard disks and thus their size can be changed, but this can be very time-consuming.

support

In addition to virtual machines such as Virtual PC and Virtual Server or operating systems such as Windows 7 , the file format is also supported by Windows Server 2008 and the Windows Automated Installation Kit , as well as by many others (some also free programs ) such as VirtualBox , Xen or 7- Zip .

The VHD format is the default file format - generally for memory dumps and particularly about for backups in the virtualization - Portfolio of Microsoft are recorded and disseminated.

With the Disk2VHD program from Windows Sysinternals , the data can be transferred from physical hard disks to virtual hard disks (images) in order to integrate them into VirtualBox , for example , and thus migrate entire computers .

Web links

References and comments

  1. ↑ a b c News about virtual hard disks in Windows 7 - Microsoft Technet ; last changed in October 2010
  2. ↑ Windows 7: Off to the VHD Part 2 ( Memento from March 24, 2011 in the Internet Archive ) - j-sys.de - Archive , on May 2, 2010
  3. ↑ a b ws08_r2_vhd_performance_whitepaper ( Memento from June 7, 2012 in the Internet Archive ) (English, docx ) - Microsoft , see p. 12 and p. 32 (accessed on June 23, 2012)
  4. ↑ Preliminary version Build 7989 of Windows 8 is circulating on the Internet - Heise , June 22, 2011; Even if Heise (probably only out of habit or negligence [copied from Microsoft]) also wrote “ Te ra byte ”, what actually means here is “ Te bi byte ” (see if necessary under “ NTFS ” with “size of a file "And" 16 TiB ").
  5. ↑ a b VHD: Guide to virtual hard disks . In: Com! , April 26, 2010
  6. ↑ Hyper-V - format of the virtual hard disk: Overview ( English ) - Microsoft TechNet , as last amended on November 1, 2013 (accessed on 14 June 2017); u. a. with "support for virtual disks with a storage capacity of up to 64 TB", wherein it is assumed here that rather the technical Te bi byte (and not customer-friendly Te ra byte ) are meant, as such limitations only Bi närsystem and ibid exist in connection with the size of so-called data types (such as 16- and 32-bit integers ) as well as sector / block sizes or the number of cylinders (see also under data block and hard disk geometry ; see also Byte # comparison table )
  7. ↑ Microsoft: Windows 8 can mount ISO and VHD files directly . In: Golem.de , on August 31, 2011; Retrieved November 19, 2013
  8. ↑ VHD Resize. In: PC Magazin , March 22, 2010
  9. ↑ Shrinking virtual hard disks . In: TechNet Blogs , March 20, 2007
  10. ↑ Windows 7 should support the VHD format ( Memento from August 26, 2010 in the Internet Archive ) - former wiki entry at Computerwoche , last changed on November 6, 2008 (last saved in the Internet archive on August 26, 2010)
  11. ↑ Virtual hard disks (VHDs) under Windows 7. In: PC-Welt , July 31, 2009
  12. ↑ Sysinternals Disk2vhd (English) - Microsoft Technet ; As of January 21, 2014