FlashCopy® is a Copy Services feature that is available with the SAN Volume Controller.
In its basic mode, the FlashCopy feature copies the contents of a source virtual disk (VDisk) to a target VDisk. Any data that existed on the target VDisk is lost and is replaced by the copied data. After the copy operation has completed, the target VDisks contain the contents of the source VDisks as they existed at a single point in time unless target writes have been performed. The FlashCopy feature is sometimes described as an instance of a time-zero copy (T 0) or point-in-time copy technology. Although the FlashCopy operation takes some time to complete, the resulting data on the target VDisk is presented so that the copy appears to have occurred immediately.
Although it is difficult to make a consistent copy of a data set that is constantly updated, point-in-time copy techniques help solve this problem. If a copy of a data set is created using a technology that does not provide point-in-time techniques and the data set changes during the copy operation, the resulting copy might contain data that is not consistent. For example, if a reference to an object is copied earlier than the object itself and the object is moved before it is copied, the copy contains the referenced object at its new location but the copied reference still points to the old location.
More advanced FlashCopy features allow operations to occur on multiple source and target VDisks. FlashCopy management operations are coordinated to allow a common single point in time for copying target VDisks from their respective source VDisks. This allows a consistent copy of data that spans multiple VDisks. The FlashCopy feature also allows multiple target VDisks to be copied from each source VDisk. This can be used to create images from different points in time for each source VDisk.
The Cascaded FlashCopy feature allows a FlashCopy target VDisk to be the source VDisk of another FlashCopy mapping.
The incremental FlashCopy feature reduces the amount of time that is required to copy the source VDisk for multiple FlashCopy mappings. The initial FlashCopy mapping copies all of the data from the source VDisk to the target VDisk. Subsequent FlashCopy mappings only copy data that has been modified since the initial FlashCopy mapping. You can define a FlashCopy mapping as incremental only when you create the FlashCopy mapping.
The multi-target reverse FlashCopy feature allows you to start a FlashCopy mapping where the target VDisk is the source VDisk in a second FlashCopy mapping. You can use this feature to reverse a FlashCopy mapping direction without having to remove existing mappings, and without losing data from the target VDisk.
A FlashCopy mapping can also be created to mirror an existing mapping; these paired mappings are called partners. A mapping can have only one partnership. For example, VDisks A and B can have two mappings; A > B and B > A.
Any VDisk that is part of a FlashCopy operation can be space-efficient. Using a space-efficient VDisk as a FlashCopy target and setting the background FlashCopy rate to 0 (nocopy) can reduce the amount of storage that is required to maintain a point-in-time copy. The source VDisks and target VDisks can also be mirrored to improve availability of the VDisks.