This invention relates to a method of, and system for, handling a FlashCopy® process. (FlashCopy is a registered trademark of International Business Machines Corporation in the United States and other countries.) In one embodiment the method can be used for reversing a FlashCopy® mapping in a cascade.
A FlashCopy® process is a feature supported on various storage devices that allows a user or an automated process to make nearly instantaneous copies of entire logical volumes of data. A copy of a source disk is made on a target disk. The copies are immediately available for both read and write access. A common feature of FlashCopy® process like implementations is the ability to reverse the copy. That is, to populate the source disk of a FlashCopy® map with the contents of the target disk. With cascaded implementations, in which a target disk later becomes the source disk for a further FlashCopy® process, this feature is complicated by the fact that the “grains” of data presented by a disk are located on a number of target/source disks “upstream” of the disk itself. This means that in order for a disk to maintain the image it is presenting, it must have access to all the disks containing these grains of data.
Reversing a FlashCopy® process is the process of ensuring that the source disk presents the same image as the target disk, at the point in time that the reverse is started. This means that the contents of the source disk need to be modified in order to maintain the correct image. Now, if all of the target disks between the source and target disks in the cascade and the target disk itself are not needed, then the reverse can be achieved by simply taking offline all the target disks and reversing the order of the source and target disks in the cascade. Although this solution is sufficient for some use cases, it drastically restricts the flexibility of the FlashCopy® implementation, because in most cases the user will be reluctant to accept the loss of their intermediate FlashCopy® images, since they may contain other valid backup copies of the original source.
It is therefore an object of the invention to improve upon the known art.