HP StorageWorks XP Remote Web Console Software - Manual (Page 128)

but may affect the storage system’s I/O performance if the P-VOL is experiencing high write I/O
activity. A lower setting (for example, 3 tracks) slows down the initial copy operation to minimize
the impact of the initial copy operation on the storage system’s I/O performance.
Priority: Specifies the order in which the initial copy operations will be performed, if the number
of requested initial copy operations is greater than the maximum initial copy activity setting on the
System Option window. The highest priority is 1, and the lowest priority is 256 (current default =
32). The XP Continuous Access initial copy priority option can be used to spread initial copy
operations across array groups and/or array domains (DKA pairs) to reduce initial copy time and
to prevent host I/O contention.
Difference management: Specifies the measurement method that XP Continuous Access uses 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 unit
(LU). See
“Difference Management” (page 19) for further information on this option.
Example: If the maximum initial copy activity setting is four, and you create six pairs at the same
time (for LUNs 000 through 005), the initial copy priority is set as follows:
Priority P-VOL of Pair
1 LUN 03
2 LUN 05
3 LUN 00
4 LUN 04
5 LUN 01, 02
The MCU immediately starts the initial copy operations for LUNs 003, 005, 000, and 004,
immediately; starts LUN 001 when one of the first four initial copy operations is complete, and
then starts LUN 002 when the next initial copy operation is complete. If more XP Continuous Access
pairs are created, the MCU also prioritizes the initial copy operations by the time requested so
that all pairs in the first group are started before any pair in the next group is started.
If the time-out error occurs during the Paircreate 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 Paircreate operation.
Pair Options
When you create new XP Continuous Access pairs, you select the pair options on the Paircreate
dialog box. You can change the fence level and error level pair options after a pair has been
added. You cannot change the difference management or CT group of an existing pair. You need
to release and then restart the pair to change these options.
P-VOL Fence Level (Synchronous only): Specifies the conditions under which the MCU will reject
write operations to the P-VOL, which is known as fencing: never, data, or status (default = Never).
This parameter is very important for disaster recovery planning (see
“Considering the P-VOL Fence
Level Setting” (page 149) ).
•
Never: The P-VOL will never be fenced. If the XP Continuous Access pair is split or suspended,
write operations to the P-VOL will be accepted. (The fence level for all XP Continuous Access
Asynchronous pairs is Never.)
•
Data: The P-VOL will be fenced when the MCU cannot successfully execute an update copy
operation for any reason.
•
Status: The P-VOL will be fenced only if the MCU is not able to change the S-VOL status to
suspended when an update copy operation fails. If the MCU changes the S-VOL status to
128 Performing XP Continuous Access Pair Operations