FlashCopy
{{Onesource|date=September 2010}}
FlashCopy is an IBM feature supported on various IBM storage devices that made it possible to create, nearly instantaneously, point-in-time snapshot copies of entire logical volumes or data sets.{{Citation | last = Connor | first = Denni |title = IBM adds teeth to shark enterprise storage system |newspaper =Network World | page = 16 | date = December 18, 2000 | url = https://books.google.com/books?id=chsEAAAAMBAJ&pg=PA16 | accessdate = September 15, 2010}} The Hitachi Data Systems implementation providing similar function was branded as ShadowImage. Using either implementation, the copies are immediately available for both read and write access.
Implementations
=Version 1=
The first implementation of FlashCopy, Version 1 allowed entire volumes to be instantaneously “copied” to another volume by using the facilities of the newer Enterprise Storage Subsystems (ESS).{{Cite web |title= FlashCopy |work= Web page |year=2007 |publisher= Recovery Specialties, LLC |url= http://recoveryspecialties.com/flashcopy.html |accessdate= July 18, 2013 }}
Version 1 of FlashCopy had limitations however. Although the copy or “flash” of a volume occurred instantaneously, the FlashCopy commands were issued sequentially and the ESS required a brief moment to establish the new pointers. Because of this minute processing delay, the data residing on two volumes that were FlashCopied are not exactly time consistent.
=Version 2=
FlashCopy Version 2 introduced the ability to flash individual data sets and then added support for “consistency groups”. FlashCopy consistency groups can be used to help create a consistent point-in-time copy across multiple volumes, and even across multiple ESSs, thus managing the consistency of dependent writes.
FlashCopy consistency groups are used in a single-site scenario in order to create a time-consistent copy of data that can then be backed-up and sent off site, or in a multi-site Global Mirror for ESS implementation to force time consistency at the remote site.
The implementation of consistency groups is not limited to FlashCopy. Global Mirror for IBM System z series (formerly known as XRC or eXtended Remote Copy) also creates consistency groups to asynchronously mirror disk data from one site to another over any distance .