The fast reverse option allows you to reverse a FlashCopy relationship without waiting for the background copy of a previous FlashCopy to finish.
In disaster recovery situations, when you use Global Mirror, you must use volumes with consistent data at the target site. Part of the setup requires that you enable the fast restore option, a copy option that is available for FlashCopy operations. (This option applies to a Global Mirror operation, which is based on existing Global Copy and FlashCopy operations at the target site.)
Use fast restore option to reverse a FlashCopy target volume and allow consistent data to be copied back to its associated source volume, without having to wait for the background copy from the original source to the original target to complete. You can then vary the volumes online and start your applications.