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For the World War II phonographic records, see V-Disc.

In storage virtualization, virtual disk (VD[1]) or vdisk is a virtual logical disk or volume with which a computer or application performs I/O operations. Generally it is provided by a storage-virtualization device that is a part of storage area network (SAN).[citation needed] As of 2012 the term vdisk is used in HP EVA disk arrays[citation needed] and in IBM SAN Volume Controller.[2]

The disk is classed as virtual due to the way it maps to the physical storage capacity it represents. Most virtual-storage systems include a meta-data mapping table which translates the incoming (virtual) disk identifier, and LBA (logical block addressing) to a physical disk identifier and LBA.

The virtualization granularity depends on the implementation. Some virtualized systems simply provide what may be thought of more as disk aggregation and so the granularity is a physical disk itself. True[weasel words] virtualization systems actually break down the physical disks into smaller "chunks", called extents.[citation needed] This allows spreading a single virtual disk across many physical disks; such parallelizing of the disk access can deliver improved performance over a non-virtualized system.

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  1. ^ Buyya, Rajkumar; Goscinski, Andrzej M., eds. (2010-12-17). Cloud Computing: Principles and Paradigms. Wiley Series on Parallel and Distributed Computing 87. John Wiley & Sons. p. 664. ISBN 9781118002209. Retrieved 2013-02-25. [...] computational resources such as virtual machines (VM), virtual application networks (VAN) and virtual disks (VD) can be ordered on demand in a matter of minutes or even seconds. 
  2. ^ http://books.google.com/books?id=zIr_5Ls9LxcC&pg=PT309.  Missing or empty |title= (help)