HP StorageWorks XP Remote Web Console Software User Manual
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number, the MCU suspends all affected XP Continuous Access (and TrueCopy for Mainframe) pairs
to prevent hosts from adversely affecting performance due to the inadequate number of paths. If
you enter a number larger than the number of paths already set on the Add RCU dialog box, or
if the number of paths falls below this number (for example, failed path), an error occurs. When
an error occurs, the MCU suspends all affected XP Continuous Access (and TrueCopy for Mainframe)
pairs to prevent remote copy operations from adversely affecting performance due to the inadequate
number of paths. If the MCU contains XP Continuous Access pairs that contain critical data for
disaster recovery, set the minimum number of paths to one, so that XP Continuous Access operations
continue even if there is only one path to an RCU. If you need high performance at the MCU, set
the minimum number of paths to two or more (up to eight per CU), depending on the number of
pairs managed by the MCU.
When you have XP Continuous Access Asynchronous pairs configured on a Fibre Channel interface,
set the same value for the Minimum Paths option for all RCUs.
CAUTION:
If XP Continuous Access pairs are suspended because the number of paths has
dropped below this setting, the P-VOL fence level pair option (see
) determines whether the XP Continuous Access Synchronous P-VOLs are fenced (that is,
reject all write operations).
The RIO MIH Time setting specifies the time value for the remote I/O (RIO) missing interrupt handler
(MIH), which is the wait time until data transfer from the MCU to RCU is complete. The RIO MIH
time value must be from 10 to 100 seconds. The default setting is 15 seconds. This setting is
available for both Fibre Channel and serial interfaces. For further information on the MIH, see the
Hitachi TrueCopy™ for Mainframe User's Guide: HP XP24000 Disk Array, HP XP20000 Disk
Array.
The Round Trip Time setting is a reference value used for automatic control of the initial copy pace
and for avoiding the remote I/O response time to the update I/Os being affected by initial copy
while the copy operation is in progress. The value of Round Trip Time is compared to the remote
I/O response time, and then, the copy pace is controlled when the difference between the two
values is large.
If the difference between the remote I/O response time and the value of Round Trip Time is large,
for example, the remote I/O response time is 500 ms but the value of Round Trip Time is 1 ms,
the copy pace will decrease or sometimes the initial copy will interrupt, so that the initial copy
process does not occupy the entire bandwidth of the line(s).
On the other hand, if the difference between the remote I/O response time and the value of Round
Trip Time is small, for example, the remote I/O response time is 5 ms and value of Round Trip
Time is 1 ms, the initial copy runs at specified pace.
The setting of Round Trip Time is available for the initial copy operation of XP Continuous Access
Synchronous and XP Continuous Access Asynchronous on the XP24000 and XP20000 disk arrays
and their succession models.
The default value of Round Trip Time is 1 ms. Specify an appropriate value for Round Trip Time
when the distance between MCU and RCU is long or there is a delay caused by the line equipment.
If the initial copy operation is performed with the default value of Round Trip Time instead of the
appropriate value, it may take unexpectedly long time to complete the initial copy operation.
You may specify 1 ms to 500 ms at the Round Trip Time. You can use the following formula to
determine the value of Round Trip Time.
Round Trip time = round trip time between MCU-RCU x 2
(*)
+ initial copy response time (ms)
(*)
A data transfer between the MCU and RCU involves two response sequences in one command
issuance. Therefore, you need to double the round trip time between the MCU and RCU.
RCU Operations
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