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

About TrueCopy for z/OS Operations 2-13
Hitachi Universal Storage Platform V TrueCopy for IBM z/OS User’s Guide
Asynchronous Consistency Groups
A TrueCopy for z/OS Async consistency group is a user-defined set of pairs
across which update sequence consistency is maintained and ensured at the
remote site. Each TCzA pair must be assigned to a consistency group. TCzA
allows you to configure up to 128 consistency groups (00-7F) for each MCU
and provides group-based operations for consistency groups (e.g., suspend
and resynchronize group). Consistency groups enable you to maintain update
sequence consistency for databases which span multiple volumes, allowing
immediate database recovery at the remote site when needed.
Host I/O Time-Stamping Function
If you plan to establish TCzA consistency groups, the I/O time-stamping
function must be installed on the host processor at the main (primary) site.
The I/O time-stamp, which is provided by MVS DFSMSdfp, is the same time-
stamp that is used by IBM XRC pairs. The RCU requires the I/O time-stamp
information to process TCzA recordsets. The I/O time-stamping function
should also be installed on the host processor at the remote (secondary) site,
so that time-stamps can be used when copying data in the reverse direction.
Note: If the main and/or remote system consists of several CPU complexes, a
SYSPLEX timer is required to provide a common time reference for the I/O
time-stamping function.
Error Reporting Communications
Error reporting communications (ERC), which transfers information between
host processors at the main and remote sites, is a critical component of any
disaster recovery effort. You can configure ERC using channel-to-channel
communications, NetView technology, or other interconnect technologies,
depending on your installation requirements and standards. Neither TCz nor
the TrueCopy for z/OS software provides ERC between the main and remote
sites.
When TCz is used as a data migration tool, ERC is recommended but is not
required. When TCz is used as a disaster recovery tool, ERC is required to
ensure effective disaster recovery operations. When a TCz pair is suspended
due to an error condition, the MCU generates sense information which results
in an IEA491E system console message. This information should be
transferred to the remote site via the ERC for effective disaster detection and
recovery.