HP XP P9000 Continuous Access Synchronous for Mainframe Systems User Guide

Main (MCU) and remote (RCU) systems
The main system manages the P-VOL and the following operations:
• Host I/O operations to the P-VOL.
• Initial copy and update copy operations between the P-VOL and S-VOL.
• Pair status and configuration information.
The remote system manages the S-VOL and the following operations:
• Remote copy operations issued by the main system.
• Assists in managing pair status and configuration (for example, rejects write I/Os to the S-VOL).
The XP P9500 CU can function simultaneously as a main system for one or more P-VOLs, and as
a remote system for one or more S-VOLs. This kind of configuration requires that data paths and
Fibre Channel ports are configured for both copy directions.
Volume pairs
As described previously, original data is stored in the P-VOL and the remote copy is stored in the
S-VOL. The pair can be suspended, re-synchronized, reverse re-synchronized, and returned to
Simplex status.
• When paired, the volumes are synchronized.
• When suspended, new data is sent to the P-VOL but not the S-VOL.
• When re-synchronized, data that changed while the pair was split is copied to the S-VOL.
• When necessary, data in the S-VOL can be copied to the P-VOL.
During normal operations, the P-VOL remains available to the host for read and write I/O operations.
The remote system rejects write I/Os for the S-VOL. The S-VOL can only be written to when the
pair is suspended and when the write-enable option is specified for the S-VOL. In this instance,
S-VOL and P-VOL track maps keep track of differential data and are used to resynchronize the
pair.
Volumes on the local and remote storage systems must be defined and formatted prior to pairing.
Data path
Cnt Ac-S Z operations are carried out between local and remote storage systems connected by a
Fibre Channel interface. The data path, also referred to as the remote copy connection, connects
ports on the local XP P9500 storage system to the ports on the remote storage system. The ports
are assigned attributes that allow them to send and receive data.
One data path connection is required, but two or more independent connections are recommended,
for hardware redundancy. A maximum of eight paths per control unit (CU) can be used.
Consistency groups
A consistency group is a grouping of pairs upon which copy operations are performed
simultaneously, and in which the pairs’ status remains consistent. A consistency group can include
pairs that reside in from one to four main and remote systems.
When you issue a Cnt Ac-S Z command on the consistency group, it is run on all pairs in the group.
The pairs’ status changes at the same time, though this depends on the group options you have
set. Some pair operations take priority under certain circumstances. Full information is covered in
“Consistency group planning” (page 40).
10 Continuous Access Synchronous Z overview