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

2-32 About TrueCopy for z/OS Operations
Hitachi Universal Storage Platform V TrueCopy for IBM z/OS User’s Guide
Pair Status
TrueCopy for z/OS displays the pair status for each volume in the selected
logical CU of the connected USP V. The MCU maintains the status of the M-VOL
and is responsible for keeping the M-VOL and its R-VOL synchronized. The RCU
maintains the status of the R-VOL. The MCU can change the pair status of the
M-VOL and R-VOL. The RCU can change the pair status of the R-VOL but not
the M-VOL. The MCU will detect when the RCU changes the R-VOL status (if
the path status is normal) and will change the M-VOL status accordingly. The
TCz pair status can be acquired from the MCU and RCU using the TCz software
(Pair Status) and the CQUERY TSO command.
Table 2-5 lists and describes the TCz pair status descriptions. A volume which
is not assigned to a TCz pair has the status simplex. When a TCz pair is
started, the MCU changes the status of both volumes (M-VOL and R-VOL) to
pending duplex. When the initial copy operation is complete, the MCU changes
the status of both volumes to duplex. When a pair is suspended from the MCU,
the MCU changes the status of the M-VOL and R-VOL (if the path status is
normal) to suspended. When a pair is suspended from the RCU, the RCU
changes the status of the R-VOL to suspended, and the MCU detects the pair
suspension (if the path status is normal) and changes the M-VOL status to
suspended. When you release a pair from the MCU, the MCU changes the
status of the M-VOL and R-VOL (if the path status is normal) to simplex. When
you release a pair from the RCU, the RCU changes the R-VOL status to
simplex, and the MCU detects the pair release (if the path status is normal)
and changes the M-VOL status to suspended.
TCzA-Specific Pair Status
The TCzA suspending and deleting transitional states occur when a request to
change TCzA pair status has been accepted, but the change to the requested
status (suspended or simplex) is not yet complete. These states are not
reported to the host. In the case of suspending, both the user and the MCU
can request the status change. In the case of deleting, only the user can
request the status change. If the user requested the status change, the final
status is reported at the end of the transition. If an error caused the status to
change to suspended, the suspended status is reported at the beginning of the
transition.
The TCzA SEQCHK status is indicated when a TCzA pair assigned to a
consistency group with the System timer type accepts a non-time-stamped
update from the primary system. The SEQCHK status does not affect TCzA
copy activities and will be removed when the next time-stamped update is
successfully copied to the R-VOL. However, if a disaster or system failure
occurs before the next time-stamped update, the update sequence consistency
between the R-VOL and other R-VOLs in the consistency group is not ensured.
To ensure effective disaster recovery, you should detect and remove the
source of the SEQCHK status. The SEQCHK status can be caused by any of the
following: