HP StorageWorks XP Remote Web Console Software - Manual (Page 66)

the DFW-to-R-VOL required option when one side of RCU cache is closed (the add pair operation
fails).
Consistency Groups
The TrueCopy for Mainframe Asynchronous consistency groups have the following requirements:
•
All TrueCopy for Mainframe Asynchronous 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 TrueCopy
for Mainframe Asynchronous groups and XP Continuous Access Asynchronous groups (for
example, 64 TrueCopy for Mainframe Asynchronous + 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 TrueCopy for Mainframe Asynchronous pairs or TCA
pairs, but not both.
•
Only TrueCopy for Mainframe Asynchronous pairs that belong to the same CLPR can be
allocated to one consistency group. For further information on CLPR, see the HP StorageWorks
XP24000/XP20000 Disk/Cache Partition User's Guide.
Restrictions on Volumes
If CSUSPEND or FREEZE command is used, TrueCopy for Mainframe M-VOLs may report SCP
(State Change Pending) to the host. If the CSUSPEND, or FREEZE command is issued to certain
volumes (for example, 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.
Assessing TrueCopy for Mainframe Requirements
Calculation of the Maximum Number of Pairs
The differential data (updated by write I/Os during suspension) between M-VOL and R-VOL is
stored in each bitmap. When a released/suspended pair is resynchronized, the MCU merges the
M-VOL and R-VOL bitmaps, and the differential data is copied to the R-VOL.
66 Preparing for TrueCopy for Mainframe Operations