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1 Overview of Compatible XRC
This topic provides an overview of the Compatible XRC (Compatible XRC) feature and configuration.
Function overview
The Compatible XRC feature (Compatible XRC) for the XP P9500 provides compatibility with IBM
Extended Remote Copy (hereinafter called "XRC") asynchronous remote copy operations for data
backup and recovery in the event of a disaster.
Compatible XRC, used in mainframe systems, has interoperability with the XRC feature and is
provided as the program product. Compatible XRC is compatible with System Data Mover (SDM)
in Data Facility Storage Management Subsystem (DFSMS), which is common to the XRC environment.
Compatible XRC operations are performed in a similar way of XRC by issuing Time Sharing Option
(TSO) commands from the host system to the logical devices on the XP P9500..
In Compatible XRC operations, the data written from the primary host at the primary site is written
to the primary volume by means of the cache memory at the primary XP P9500 disk array. At the
same time, the data is temporarily stored in cache memory as 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 shows an overview of Compatible XRC operations.
Figure 1 Overview of Compatible XRC operations
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 reinitiated 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 XP P9500 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.
Function overview
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