HP XP7 Storage - Manual (Page 5)

1 Overview of Compatible XRC
This topic provides an overview of the Compatible XRC (Compatible XRC) feature and configuration.
Introducing Compatible XRC
In Compatible XRC operations, the data written from the host to the primary volume in the primary
HP XP7 Storage disk array is also written temporarily to a section of cache memory in the HP XP7
Storage system called a sidefile. At the secondary site, the System Data Mover (SDM) software
asynchronously reads the sidefile data over communication lines from the primary storage system
at the primary site. SDM then writes the data to the secondary volume in the secondary storage
system in the same order as it was written at the primary site.
SDM manages pair definitions of the primary and secondary storage systems or pair definitions
of the primary and secondary volumes.
The following figure shows an overview of Compatible XRC operations.
Features of Compatible XRC
The Compatible XRC feature (Compatible XRC) for HP XP7 Storage provides compatibility with
IBM Extended Remote Copy (XRC) asynchronous remote copy operations for data backup and
recovery in the event of a disaster.
Compatible XRC, used in mainframe systems, interoperates with System Data Mover (SDM) in the
Data Facility Storage Management Subsystem (DFSMS) in an XRC environment. Compatible XRC
operations are similar to XRC operations, issuing Time Sharing Option (TSO) commands from the
host system to logical devices on the HP XP7 Storage system.
Sessions
In Compatible XRC operations, a group of primary volumes is processed as one session. Data is
written to the secondary volumes in each session in the same order as it was written at the primary
site. In the event of a failure, all volume pairs in the same session are suspended. The write operation
is not performed due to the failure. However, the write order (sequence) is maintained so that the
write process can be re-initiated after recovery.
A session is further divided into internal sessions called storage control (SC) sessions for each
volume. SDM reads the data written to the HP XP7 Storage disk array at the primary site in order
of time stamp in each SC session. SDM checks the time stamp of each SC session, and determines
in what order the data is written to the secondary volumes. Data is written to the secondary volumes
in units of session in the same order as it was written at the primary site, not in units of SC session.
Introducing Compatible XRC 5