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

2-28 About TrueCopy for z/OS Operations
Hitachi Universal Storage Platform V TrueCopy for IBM z/OS User’s Guide
TrueCopy for z/OS Async Consistency Group Operations
TrueCopy for z/OS Async consistency groups enable update sequence
consistency to be maintained across a group of volumes. The R-VOLs of the
pairs in a consistency group must be located within one RCU (n-to-1
requirement). The TCzA consistency group operations include:
• Group options
• Group consistency time
• Group operations.
Group Options
TrueCopy for z/OS Async provides the following options for each consistency
group: Timer Type, Copy Pending timeout, and RCU Ready Timeout.
These options are selected when you add a group. If you want to change the
timeout options of a group, you must suspend all pairs in the group first. If
you want to change the Timer Type option, you must release all pairs. The
Timer Type option Copy Pending timeout option must be the same for all
MCUs which contain M-VOLs in the group. The RCU Ready timeout option can
be different at each MCU if desired.
Timer Type. This group option determines how the MCU will acquire the time-
stamp for the TCzA recordsets:
• System. When the System timer option is selected, the MCU acquires the
time-stamp information for each recordset as follows. When a TCzA pair is
established, the MCU reports state-change-interrupt (SCI) to all hosts. The
host then issues a series of sense group commands to determine the device
status change, and the MCU returns the same response as if the device had
been added to an XRC session to activate I/O time-stamping for the device.
Once I/O time-stamping is activated, the MVS IOS routine attaches the time-
stamp information (contents of time-of-day (TOD) clock) to each write I/O
operation for the device. The time-stamp indicates the time that the update
was generated during start subchannel (SSCH) at the main host system, and
the time-stamp is transferred to the MCU at the beginning of each I/O
operation.
• Local. The Local timer option enables the MCU to generate the time-stamp
for each update I/O using its own internal clock, rather than using the SMS
I/O time-stamp.
• None. The None timer option should only be selected when establishing
TCzA pairs in the reverse direction (from secondary to primary). When the
None option is selected, the MCU still acquires the time-stamp information
from the host I/O time-stamping function.