ForensicsWiki will continue to operate as it has before and will not be shutting down. Thank you for your continued support of ForensicsWiki.

Difference between pages "Disk Imaging" and "Virtual Hard Disk (VHD)"

From ForensicsWiki
(Difference between pages)
Jump to: navigation, search
(Selective imaging)
 
 
Line 1: Line 1:
 
{{expand}}
 
{{expand}}
  
Disk imaging is the process of making a bit-by-bit copy of a disk. Imaging (in more general terms) can apply to anything that can be considered as a bit-stream, e.g. a physical or logical volumes, network streams, etc.
+
Used by:
 +
* Microsoft Virtual PC
 +
* Microsoft Virtual Server
 +
* Microsoft Hyper-V Server
  
The most straight-forward disk imaging method is reading a disk from start to end and writing the data to a [[:Category:Forensics_File_Formats|Forensics image format]].
+
== Image types ==
This can be a time consuming process especially for disks with a large capacity.
+
There are multiple types of Virtual Hard Disk (VHD) images:
 +
* Fixed-size hard disk image; the image contains all data
 +
* Dynamic-size (or sparse) hard disk image; the image contains used data only
 +
* Differencing (or delta) hard disk image; the image contains changes relative to its parent image
  
== Hardware solutions ==
+
== Snapshots ==
 +
Snapshot Differencing Disk file (AVHD)
  
== Software solutions ==
+
== See Also ==
 +
* [[Disk Images]]
  
== Compressed storage ==
+
== External Links ==
  
A common technique to reduce the size of an image file is to compress the data.
+
* [http://en.wikipedia.org/wiki/VHD_(file_format) VHD (file format)], by Wikipedia
On modern computers, with multiple cores, the compression can be done in parallel reducing the output without prolonging the imaging process.
+
* [http://technet.microsoft.com/en-us/library/bb676673.aspx Virtual Hard Disk Image Format Specification], by Microsoft, October 2006
Since the write speed of the target disk can be a bottleneck in imaging process parallel compression can reduce the total time of the imaging process.
+
[[Guymager]] was one of the first imaging tools to implement the concept of multi-process compression for the [[Encase image file format]]. This technique is now used by various imaging tools including [http://www.tableau.com/index.php?pageid=products&model=TSW-TIM Tableau Imager (TIM)]
+
 
+
Other techniques like storing the data sparse or '''empty-block compression''' can reduce the total time of the imaging process and the resulting size of new non-encrypted (0-byte filled) disks.
+
 
+
== Error tolerance and recovery ==
+
 
+
== Smart imaging ==
+
Smart imaging is a combination of techniques to make the imaging process more intelligent.
+
* Deduplication
+
* Selective imaging
+
* Decryption while imaging
+
 
+
=== Deduplication ===
+
Deduplication is the process of determining and storing data that occurs more than once on-disk, only once in the image.
+
It is even possible to store the data once for a corpus of images using techniques like hash based imaging.
+
 
+
=== Selective imaging ===
+
Selective imaging is a technique to only make a copy of certain information on a disk like the $MFT on an [[NTFS]] volume with the necessary contextual information.
+
 
+
[[EnCase]] Logical Evidence Format (LEF) is an example of a selective image; although the format can only handle a limited set of contextual information.
+
 
+
=== Decryption while imaging ===
+
Encrypted data is worst-case scenario for compression. Because the encryption process should be deterministic a solution to reduce the size of an encrypted image is to store it non-encrypted and compressed and encrypt it on-the-fly if required. Although this should be rare since the non-encrypted data is what undergoes analysis.
+
 
+
== Also see ==
+
[[:Category:Forensics_File_Formats|Forensics File Formats]]
+
 
+
== External Links ==
+
* [http://www.tableau.com/pdf/en/Tableau_Forensic_Disk_Perf.pdf Benchmarking Hard Disk Duplication Performance in Forensic Applications], by [[Robert Botchek]]
+
  
=== Hash based imaging ===
+
[[Category:File Formats]]
* [http://www.dfrws.org/2010/proceedings/2010-314.pdf Hash based disk imaging using AFF4], by [[Michael Cohen]], [[Bradley Schatz]]
+

Revision as of 15:41, 14 September 2012

Information icon.png

Please help to improve this article by expanding it.
Further information might be found on the discussion page.

Used by:

  • Microsoft Virtual PC
  • Microsoft Virtual Server
  • Microsoft Hyper-V Server

Image types

There are multiple types of Virtual Hard Disk (VHD) images:

  • Fixed-size hard disk image; the image contains all data
  • Dynamic-size (or sparse) hard disk image; the image contains used data only
  • Differencing (or delta) hard disk image; the image contains changes relative to its parent image

Snapshots

Snapshot Differencing Disk file (AVHD)

See Also

External Links