Hitachi TrueCopy for IBM z/OS User and Reference Guide (T5211-96001, June 2007)
About TrueCopy for z/OS Operations 2-35
Hitachi Universal Storage Platform V TrueCopy for IBM z/OS User’s Guide
Suspended Pairs
Table 2-6 lists and describes the TCz suspend types, which indicate the reason
for suspension. A TCz pair can be suspended by the user at any time after the
initial copy operation is complete. The user must suspend a TCz pair in order
to perform ICKDSF maintenance on the M-VOL or to access the R-VOL (read
only mode). TCz pairs are also suspended when the CGROUP/ RUN command
is processed. When a TCz Synchronous pair is suspended by the user, the MCU
ensures synchronization by completing any pending update copy operation
before changing the status to suspended. When a TCzA pair is suspended by
the user, the MCU and RCU ensure synchronization by either completing or
discarding any pending update copy operations according to the user-specified
drain/purge suspend option.
A TrueCopy for z/OS pair is suspended by the MCU when the following
suspension conditions are detected. A TCzA pair can also be suspended by the
RCU.
When the MCU detects that the user has released the pair from the RCU
(e.g., to access an R-VOL at the remote site)
When the MCU detects an error condition related to the RCU, R-VOL, a TCz
Synchronous update copy operation or a TCzA recordset operation
When the RCU cannot execute DFW (DASD fast write) to the R-VOL (only if
DFW required is selected)
When the MCU is unable to communicate with the RCU
If a TCz Synchronous update copy operation fails, the MCU maintains exact
synchronization by reporting a unit check and decommitting the M-VOL
update, so that the host system and application program regard that write
operation to the M-VOL as failed.
When a TCz pair is suspended, the MCU stops performing update copy
operations to the R-VOL. For a suspended TCz Synchronous pair, the MCU may
or may not continue accepting write I/Os for the M-VOL depending on the M-
VOL fence level and suspend option (if user-requested). If the MCU accepts
write I/Os for a suspended M-VOL, the MCU records the data in the M-VOL
tracks that are updated while the pair is suspended as the differential data. For
a suspended TCzA pair, the MCU and RCU keep track of any recordsets that
were discarded during suspension, and the MCU continues accepting write I/Os
for the M-VOL and records the data in the M-VOL tracks that are updated while
the pair is suspended as the differential data.
A suspended TCzA R-VOL has an additional status called the consistency status
which is displayed only at the RCU. The consistency status of a suspended
TCzA R-VOL indicates its update sequence consistency with respect to the
other R-VOLs in the same group. Table 2-7 lists and describes the consistency
status descriptions for suspended TCzA R-VOLs.