Hitachi TrueCopy for IBM z/OS User and Reference Guide (T5211-96001, June 2007)

Preparing for TrueCopy for z/OS Operations 3-9
Hitachi Universal Storage Platform V TrueCopy for IBM z/OS User’s Guide
Consistency Groups
The TCzA consistency groups have the following requirements:
• All TCzA pairs must be assigned to one and only one consistency group.
• The maximum number of pairs in one consistency group is 4096.
• The maximum number of consistency groups established for one MCU-RCU
pair is 128. The RCU supports a maximum of 128 groups. This limit of 128
groups includes both TCzA groups and TC Asynchronous groups (e.g., 64
TCzA + 64 TCA).
• Each update I/O to the M-VOLs in one consistency group must be time-
stamped using a common timer facility. The primary host system cannot
access pairs of the same consistency group if the pairs do not have a
common timer reference.
• A consistency group must consist of TCzA pairs or TCA pairs, but not both.
• Only TCzA pairs that belong to the same CLPR can be allocated to one
consistency group. For further information on CLPR, please refer to the
Virtual Partition Manager User's Guide.
Restrictions on Volumes
If CSUSPEND or FREEZE command is used, TCz M-VOLs may report SCP (State
Change Pending) to the host. If the CSUSPEND, or FREEZE command is issued
to certain volumes (e.g., active SPOOL, PAGE, or CATALOG datasets, active
SYSRES volume), the attached host(s) may enter a deadlock condition and
may require a storage control IML to correct the condition.