SRDF/Metro allows a remotely replicated (SRDF) secondary device
to be read/write accessible to the host, taking on the external
identity of the primary device (geometry, device WWN, and so on).
Both the primary and secondary devices may then appear as a single
virtual device across the two SRDF paired arrays. With both devices
being accessible, the host can read and write to both primary and
secondary devices, with SRDF/Metro ensuring each copy remains current
and consistent, addressing any write conflicts which may occur.
This patch adds this functionality to the VMAX cinder driver.
Change-Id: Ib31763ea5759f7f9c0d2e2db68ba3820188245db
Partially-Implements: blueprint vmax-replication-enhancements