Create A Global Mirror Environment; Consistency Group - IBM System storage DS6000 Series Redbook

When you start or resume a session, Consistency Groups are created, and the Master
storage disk subsystem controls the session by communicating with the Subordinate storage
disk subsystems.
There is also a session concept at the LSS level. But all LSS sessions are combined and
grouped together within a Global Mirror session.
Master
The Master is a function inside a primary storage disk subsystem that communicates with
Subordinates in other storage disk subsystems, and controls the creation of Consistency
Groups while managing the Global Mirror session. The Master is defined when the start
command for a session is issued to any LSS in a primary storage disk subsystem. This
determines who becomes the Master storage disk subsystem.
The Master needs communication paths over Fibre Channel links to any one of the LSSs in
each Subordinate disk storage server.
Subordinate
The Subordinate is a function inside a primary storage disk subsystem that communicates
with the Master and is controlled by the Master. At least one of the LSSs of each Subordinate
primary storage disk subsystems needs Fibre Channel communication paths to the Master.
This enables the communication between the Master and the Subordinate, and is required to
create Consistency Groups of volumes that spread over more than one storage disk
subsystem.
If all the volumes of a Global Mirror session reside in one primary storage disk subsystem, no
Subordinate is required, because the Master can communicate to all LSSs inside the primary
storage disk subsystem.

Consistency Group

This is a group of volumes in one or more secondary storage disk subsystems whose data
must be kept consistent at the remote site.
Local Site
This is the site that contains the production servers. This and other publications use this term
interchangeably with the terms primary, production, or source site.
Remote Site
This is the site that contains the backup servers of a disaster recovery solution. This and
other publications use this term interchangeably with the terms secondary, backup, standby,
or target site.

23.2 Create a Global Mirror environment

The following section recommends a certain sequence of steps to establish a Global Mirror
environment. This is independent of the interface used to create a Global Mirror environment.
Note that for illustration purposes, parameters and keywords are used in this section that
apply to TSO commands or to the ANTRQST macro interface. ICKDSF does use different
keywords that are described in 24.5, "Global Mirror management using ICKDSF" on
page 313.
We explain a basic Global Mirror setup, illustrated in Figure 23-1 on page 270.
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Chapter 23. Global Mirror options and configuration