HP StorageWorks XP Remote Web Console Software - Manual (Page 13)

2 Overview of XRC for Mainframe
Operations
Function Overview
In XRC for Mainframe operations, the data written from the primary host at the primary site is written
to the primary volume via cache memory at the primary disk subsystem. At the same time, it is stored
on the cache memory as a temporary sidefile. SDM, which is host software typically installed at the
secondary site, reads the sidefile data from the primary disk subsystem at the primary site
asynchronously via communication lines. SDM then writes the data to the secondary volume in the
secondary disk subsystem in the same order as it was written at the primary site.
SDM manages pair definitions of the primary and secondary disk subsystems, or pair definitions of
the primary and secondary volumes.
The following figure shows the overview of the operations.
Figure 1 Overview of XRC for Mainframe Operations
Sessions
In XRC for Mainframe 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 logical volume pairs in the same session will be suspended while the
write order is maintained.
A session is further divided into internal sessions called “storage control sessions” (SC sessions). SDM
reads the data written to the disk subsystem 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 should
Hitachi Extended Remote Copy for Mainframe user guide 13