FlashCopy
A feature of mainframe disk systems that makes an almost instant copy of a dataset or volume, as it was at one moment.
Also written point-in-time copy, snapshot, volume snapshot
FlashCopy is a disk system feature that copies data almost instantly. You ask for a copy of a volume or a dataset, and within seconds the copy is ready to use, even if it is very large.
It works by doing the real copying afterwards. At the moment of the request, the disk system records which tracks belong to the copy. Both the original and the copy can be used at once. If either is changed before a track has been copied, the disk system first saves the old version, so the copy always shows the data exactly as it was at that moment.
This changes how backups fit into batch. Instead of stopping an application for an hour while its data is backed up, a site can pause it for a few seconds, take a FlashCopy, restart the application, and back up the copy later. It is also used to refresh test systems with recent copies of data.
FlashCopy is usually requested through DFSMSdss or other storage software rather than directly. Storage administrators set it up.
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- DFSMSdssDFSMS data set services: the z/OS program for copying, moving, backing up and restoring datasets and whole volumes.
- DASDDirect access storage device, the mainframe term for disk storage.
- Disaster recoveryThe plans, copies of data and second systems that let an organisation keep running if a whole data centre is lost.
- VolumeA single unit of disk storage with a six-character label, on which datasets are placed.
- Batch windowThe period, usually overnight, in which batch work has to finish before the business needs the systems back.