HP XP P9500 Storage - Manual (Page 8)

Figure 1 ESAM components
P9500 storage systems
ESAM operations are conducted between two P9500 (P9500) systems on the primary and secondary
sites. The primary system consists of the main control unit (MCU) and service processor (SVP). The
secondary storage system consists of the remote control unit (RCU) and SVP.
The primary storage system communicates with the secondary storage system over dedicated Fibre
Channel remote copy connections.
Main and remote control units
Like Continuous Access Synchronous, ESAM replication relationships exist at the Logical Control
Unit (LCU) level within the storage systems.
•
Primary storage system LCUs containing the production volumes to be replicated are called
MCUs (main control units).
•
Secondary storage system LCUs containing the copy volumes are called RCUs (remote control
units).
Normally the MCU contains the P-VOLs and the RCU contains the S-VOLs.
The MCU communicates with the RCU via the data path. The LCU can function simultaneously as
an MCU and as an RCU. In this case, you can simultaneously set the P-VOL of one pair and the
S-VOL of another pair in the same LCU.
Pair volumes
Original data from the host is stored in the P-VOL; the remote copy is stored in the S-VOL. Data is
copied as it is written to the P-VOL; new updates are copied only when the previous updates are
acknowledged in both primary and secondary volumes.
Once a pair is created, it can be split—which suspends copy activity, resynchronized—which
restores and maintains synchronization, and deleted—which removes the pair relationship, though
not the data.
Quorum disk
The quorum disk is a continuously updated volume that contains information about the state of data
consistency between the P-VOL and S-VOL. The information is used by ESAM in the event of failure
to direct host operations to the secondary volume. The quorum disk is located in an externally
attached storage system.
8 External Storage Access Manager overview