FlashCopy is part of IBM’s Copy Services. It can be used on enterprise subsystems like the DS series and ESS devices. FlashCopy works on extents and full volume copy. The maximum number of FlashCopy sessions per volume is 255. Data set level FlashCopy extents can be on more than one volume. FlashCopy Relationship is used to refer to all the individual source and target FlashCopy pairs that are required to form a volume or data set copy.
FlashCopy enables you to make copies of a set of tracks, with the copies immediately available for read or write access. This set of tracks can consist of an entire volume, a data set, or just a selected set of tracks.
FlashCopy has the following phases:
The Establish phase is very fast, it just involves setting up pointers to a bitmap mask. Once it is complete, the source and target disks can be accessed independently. From an application's point of view, the copy is complete once the Establish phase is over. This is sometimes called the T0 data position.
The way the Copy phase is performed depends on if FlashCopy is running in Copy or NoCopy mode.
The Termination phase can happen automatically once all the data from the source has been copied over, or as a response to a FCWITHDRAW command or Withdr FlashCopy line action. At this time, there is no longer a FlashCopy relationship between source and target, they are independent volumes again.
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