Actually BCV are hypervolumes into Symmetrix or DMX box that can be used for business continuity through EMC Timefinder solutions. You can synchronizing a STD volume with a BCV volume with an establish, and splitting them when you want consistency. SRDF is a solution for Disaster recovery that needs of at least two sym or dmx box, FC connections, EMC software. You'll have and R1 volume and an R2 volume that will be synchronized.
IT's only a short picture of these powerful technologies.
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