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

6-10 Performing TrueCopy for z/OS Pair Operations
Hitachi Universal Storage Platform V TrueCopy for IBM z/OS User’s Guide
LDEVs 01, 02 5 complete. If additional TCz pairs are added, the
MCU also prioritizes the initial copy operations by
time requested, so that all TCz pairs in the first
group are started before any pair in the next
group is started.
Note: The CESTPAIR TSO command does not support the initial copy priority
option. When CESTPAIR is used to establish TCz pairs, the initial copy
operations are performed in the order that the CESTPAIR commands are
issued.
Note: If the time out error occurs during the Add Pair operation, the copy
operation may not be executed correctly in the order that you have set with
the Priority parameter. The time out error may be caused by the CU
configuration or a remote copy path error. Review the error, release the pair
with the error, and then retry the Add Pair operation.
Difference management. Specifies the measurement method that TrueCopy
for z/OS will use to manage the differential data for the pair: auto, cylinder,
or track. The default setting is Auto. When you select Auto, either Cylinder
or Track is selected depending on the basic size of the logical volume image.
DFW to R-VOL (TrueCopy for z/OS Sync only). Specifies whether the MCU will
suspend a TCz pair when the RCU cannot execute DFW to the R-VOL:
• DFW not required: the MCU will not suspend the TCz pair when DFW on
the RCU is blocked. This option is recommended if you need to maintain
synchronization of the TCz pair. Note: If a TCz pair is established using PPRC
commands, the DFW to R-VOL option is set to not required.
• DFW required: the MCU will suspend the pair when DFW on the RCU is
blocked. This option is recommended if you need to maintain high MCU I/O
performance.
Caution: The interaction of the DFW required setting and the M-VOL
fence level setting can cause a host application to fail with a permanent I/O
error when attempting to update an M-VOL. Keep track of which pairs have
the DFW required setting, and make sure that DFW to the R-VOL is not
blocked.
Note: The DFW to R-VOL setting does not affect the I/O performance of
the M-VOLs. If one side of cache is closed due to an RCU failure, the TCz
copy operation still uses DFW. The only difference between not required
and required is that new pairs cannot be established with the DFW-to-R-
VOL required option when one side of RCU cache is closed (the add pair
operation fails).
C/T Group (TrueCopy for z/OS Async only). Specifies the consistency group
for the pair(s) being added. All TCzA pairs must be assigned to a consistency
group. Note: The CESTPAIR command can be used to start TCzA pairs and
assign them to groups, but the groups must already be configured (using the
Add C/T Group dialog box.