A data storage system includes at least first, second and third virtual storage volumes, the second and third virtual storage volumes being remotely coupled as a PPRC pair to enable a mirroring of data therebetween. The storage system is responsive to a snapshot command from a host processor, to cause...http://www.google.de/patents/US6237008?utm_source=gb-gplus-sharePatent US6237008 - System and method for enabling pair-pair remote copy storage volumes to mirror data in another storage volume
