When you create a FlashCopy® image, you specify the fileset to be copied. The FlashCopy image operation is performed individually for each fileset. While the FlashCopy image is being created, all data remains online and available to users and applications. The space used to keep the FlashCopy image is included in its overall fileset space; however, a space-efficient algorithm is used to minimize the space requirement. The FlashCopy image does not include any nested filesets within it. Also, you can create incremental FlashCopy images to be used as the basis for incremental backups. You can create and maintain a maximum of 32 FlashCopy images of any fileset.
When creating a FlashCopy image for a fileset, you can indicate whether the oldest image should be deleted if creating a new one causes the maximum number of images to be exceeded. Once a FlashCopy image is created, its name cannot be changed.
The actual files in a fileset and the FlashCopy images of the files in the fileset share the same file data blocks until a client makes changes to the files. When a client makes a change to a file, such as adding or deleting data, the client performs an operation called copy on write, in which the client writes the changed blocks to a new location on disk. At this point, the FlashCopy image points to the old blocks, and the actual file points to the blocks with the new data. Therefore, any access to the FlashCopy image produces the data blocks as they existed when the FlashCopy image was created, and any access to the actual file accesses the new data blocks.
Parent topic: FlashCopy images