ESS storage subsystems support synchronous PPRC at a distance of up to 103 km. You can configure other IBM® storage subsystems to support ESCON® ports (connected by multimode fiber optic cables) at distances of up to three kilometers. ESCON Directors, if your configuration includes them, can have Extended Distance Feature (XDF) ports with singlemode fiber-optic cables for longer link lengths.
You can use 9036 ESCON Remote Channel Extenders to convert from multimode fiber links to XDF and back, and as XDF extender links. Use these or other comparable repeaters when the distance between systems is greater than 3 km and your configuration does not include ESCON Directors.
You can only dynamically switch one ESCON Director within a path to an I/O unit. The other ESCON Director, if present, provides a static connection. Refer to the appropriate storage subsystem planning guide for information about ESCON configurations with ESCON Directors.
Recovery site storage subsystems must have access to the host systems that will run primary applications when the primary system is out of service. A host system at the recovery site must be able to issue recovery commands as part of recovery system takeover procedures.