Overview of FlashCopy

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 provides both source volume to target volumes support, which came with FlashCopy Version 1, and source data set level to target data set level support, which comes with FlashCopy Version 2. FlashCopy can be used in combination with XRC, synchronous PPRC, and PPRC-XD.

The primary objective of FlashCopy is to create a copy of a source volume on the target volume. This copy is called a point-in-time copy. Access to the point-in-time copy of the data on the source volume is through reading the data from the target volume. The actual point-in-time data that is read from the target volume might or might not be physically stored on the target volume. As soon as a FlashCopy relationship is established (more specifically, as soon as the initialization process for a FlashCopy establish, initiated with the FCESTABL command, is complete), the point-in-time data is available for reading from the target volume. However, if data is written to a track that is a target track in a FlashCopy relationship and the updated target track is read afterwards, the data that is returned is user-updated data, and not the point-in-time source track data. Target tracks are withdrawn from a FlashCopy relationship as soon as any application writes to these tracks.

FlashCopy V1 requires the entire source volume and target volume to be involved in a FlashCopy relationship, even if selected tracks were specified on the FCESTABL command. FlashCopy V1 relationships do not allow any other FlashCopy relationships to exist on either the source or target volume.

ESS FlashCopy Version 2 enhances the FlashCopy function by providing an alternative method to copying an entire source volume to a target volume. This enhancement includes the following features:

Multiple FlashCopy relationships are allowed on a volume.
Track relocation is possible because for tracks to be copied, the target tracks do not need to be in the same location on the target volume as on the source volume.
A FlashCopy target and source volume need not be in the same logical subsystem (LSS) in an ESS. However, FlashCopy must be processed in the same ESS.
Extent level (data set level) FlashCopy.
Incremental/Persistent Flashcopy.
NOCOPY to COPY conversion.

Guidelines: Do not use the TSO or the API FlashCopy functions to copy data sets that you intend to access from the target volume. With FlashCopy, TSO or API usage does not provide any data management services, such as allocation or cataloging. Data sets that are copied using these functions are not accessible from the target volume without the user manually performing these data management tasks. You can use a data set copy program that provides these data management services as part of the copy process, such as DFSMSdss.