All of the XRC sessions coupled in the master session continuously
write to and read from the master data set. This access allows communication
between hosts when data is copied from the primary site to the recovery
site.
When evaluating the resources you need to successfully configure
a CXRC environment, you must plan so that all primary hosts and recovery
hosts have access to the master data set.
Rules: You must follow these conditions in
order to create the necessary access:
- Catalog the master data set and make it accessible to each host
system that processes a coupled session, as well as to the system
that processes the XRECOVER command. The master data set name is mhlq.XCOPY.msession.MASTER.
- Ensure that the master data set does not reside on the same volume
as the control data set and the volume that contains the journal data
sets.
- Allocate the master data set without defining secondary extents.
- Allocate the master data set as physical sequential and not striped.
- Allocate the master data set with contiguous tracks as the I/O
is assumed not to span multiple extents. Access to the master data
set is controlled using GRS enqueues, and therefore, all systems with
coupled SDMs must be in the same GRS configuration.
- Allocate the master data set on a single disk device.
- Ensure that the required size of the master data set is one cylinder,
which allows 14 XRC sessions to be coupled. The required size of the
master data set is fixed, which also fixes the maximum number of sessions
that can be coupled into one master session.
- Preallocate the master data set size before use of the XCOUPLE
command. Only the space that is allocated at the time the XCOUPLE
ADD command is issued is available for XRC use.
- Protect the master data set from unauthorized use.
- Do not allocate the master data set in the Extended
Address Space (EAS) of an Extended Address Volume (EAV).
Allocate the master data set with one cylinder primary space and
zero cylinders secondary space as follows:
DCB=(RECFM=FB,LRECL=15360,BLKSIZE=15360,DSORG=PS),SPACE=(CYL,(1,0))
For additional information about protecting the master data set
using RACF®, refer to Controlling access to XRC commands.
For additional information about configuring the master data set,
refer to Specifying the master data set.