HP StorageWorks XP Remote Web Console Software - Manual (Page 150)

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 Mainframe 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 Mainframe Sync only). Specifies whether the MCU will suspend a
TrueCopy for Mainframe pair when the RCU cannot execute DFW to the R-VOL:
•
DFW not required: the MCU will not suspend the TrueCopy for Mainframe pair when DFW
on the RCU is blocked. This option is recommended if you need to maintain synchronization
of the TrueCopy for Mainframe pair.If a TrueCopy for Mainframe 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.
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 TrueCopy for Mainframe 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 Mainframe Async only). Specifies the consistency group for the pair(s)
being added. All TrueCopy for Mainframe Asynchronous pairs must be assigned to a consistency
group.
The CESTPAIR command can be used to start TrueCopy for Mainframe Asynchronous pairs and
assign them to groups, but the groups must already be configured (using the Add C/T Group
dialog box).
Pair Options
When you add new TrueCopy for Mainframe pairs, you select the pair options on the Add Pair
dialog box. You can change the fence level, CFW data, and error level pair options after a pair
has been added. You cannot change the difference management, DFW to R-VOL, or CT group of
an existing pair. You need to release and then restart the pair to change any of these options.
M-VOL Fence Level (TrueCopy for Mainframe Synchronous only). Specifies the conditions under
which the MCU will reject write operations to the M-VOL, which is known as fencing. This option
is very important for disaster recovery planning. TrueCopy for Mainframe Asynchronous M-VOLs
are never fenced.
•
Data: the M-VOL will be fenced when the MCU cannot successfully execute an update copy
operation for any reason. This setting is functionally equivalent to the CRIT(YES-ALL) parameter
for the CESTPAIR command.
•
Status: the M-VOL will be fenced only if the MCU is not able to change the R-VOL pair status
to suspended when an update copy operation fails. If the MCU changes the R-VOL pair status
to suspended, subsequent write operations to the M-VOL will be permitted, and the MCU will
150 Performing TrueCopy for Mainframe Pair Operations