Difference between pages "Advanced Format" and "Virtual Hard Disk (VHD)"

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(The Problem: Death of LBA 63)
 
(Image types)
 
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=The Technology=
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{{expand}}
Hard drive manufacturers have moved to a new standard: 4KB (4,096 bytes) sectors, replacing 512B sectors. This is a good thing; it means that the signal-to-noise ratio improves, and less space is needed for error correction. Long-term improvements in speed, density, and overall capacity. Western Digital has started releasing drives with 4KB sectors under the name "Advanced Format" (not to be confused with the [[Advanced Forensics Format]]).
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=The Standard=
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== Image types ==
ATA 7 (T13/D1532, INCITS 397-2005) introduced Long Physical Sector (LPS) and Long Logical Sector (LLS) feature sets. Drives with large sector sizes shall report the actual physical/logical size in words 106 and 117-118 of the ATA IDENTIFY data.
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There are multiple types of Virtual Hard Disk (VHD) images:
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* Fixed-size hard disk image
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* Dynamic-size (or sparse) hard disk image
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* Differencing (or delta) hard disk image
  
Some Western Digital drives with "Advanced Format" reportedly do not provide the information about physical sector size (see [[#External_Links|External Links]]).
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== External Links ==
  
=The Problem: Death of LBA 63=
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* [http://en.wikipedia.org/wiki/VHD_(file_format) VHD (file format)], by Wikipedia
Operating systems written before the transition, particularly XP, have trouble with the new drives. XP makes an assumption about where the format should start (LBA 63), but this doesn't work well with the translation software that maps from logical 512B blocks to physical 4K blocks.
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* [http://technet.microsoft.com/en-us/library/bb676673.aspx Virtual Hard Disk Image Format Specification], by Microsoft
  
The nutshell is that XP should not be used to format these drives, and some assumptions made by tools and users need to be corrected. For analysis purposes, note that you can't assume that an NTFS partition starts at LBA 63. If you are used to using, for example, the Sleuthkit command "fls -o 63 <image>", this may need to change. Hopefully more information about these drives will come forth as time progresses.
 
  
LBA 63 was dying anyway.  Windows Vista and Windows 7 both align to LBA 2048 by default.  This change happened before the Advanced Format 512e drives hit the marketplace.
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[[Category:File Formats]]
 
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=The Solution=
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To format one of these drives properly for Windows XP, use the following utility (this applies only to drives from Western Digital):
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[http://www.wdc.com/en/products/advancedformat/ Western Digital Advanced Drive Format Utility]
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=External Links=
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*[http://www.anandtech.com/storage/showdoc.aspx?i=3691 A Good Overview at AnandTech]
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*[http://www.wdc.com/wdproducts/library/WhitePapers/ENG/2579-771430.pdf PDF White Paper]
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*[http://www.tomshardware.com/reviews/green-terabyte-1tb,2078-2.html A Tom's Hardware Review of the WD Caviar Green Drives]
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*[https://ata.wiki.kernel.org/index.php/ATA_4_KiB_sector_issues ATA 4 KiB sector issues (good summary from Linux ATA wiki)]
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*[http://lwn.net/Articles/377895/ 4K-sector drives and Linux (LWN.net)]
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*[http://sourceforge.net/apps/trac/smartmontools/ticket/62 WD6400AARS-00Y5B1 does not provide sector size info (smartmontools ticket)]
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Revision as of 04:01, 13 September 2012

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Further information might be found on the discussion page.

Image types

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

  • Fixed-size hard disk image
  • Dynamic-size (or sparse) hard disk image
  • Differencing (or delta) hard disk image

External Links