FlashCopy mapping

A mapping defines the relationship between a source volume and a target volume.

The FlashCopy® feature makes an instant copy of a volume at the time that it is started. To create an instant copy of a volume, you must first create a mapping between the source volume (the disk that is copied) and the target volume (the disk that receives the copy). The source and target volumes must be of equal size.

A mapping can be created between any two volumes in a system. The volumes do not have to be in the same I/O group or pool. When a FlashCopy operation starts, a checkpoint is made of the source volume. No data is copied at the time a start operation occurs. Instead, the checkpoint creates a bitmap that indicates that no part of the source volume has been copied. Each bit in the bitmap represents one region of the source volume. Each region is called a grain.

After a FlashCopy operation starts, read operations to the source volume continue to occur. If new data is written to the source or target volume, the existing data on the source is copied to the target volume before the new data is written to the source or target volume. The bitmap is updated to mark that the grain of the source volume has been copied so that later write operations to the same grain do not recopy the data.