HP StorageWorks XP24000 Continuous Access Software User and Reference Guide, v01 (T5278-96002, June 2007)

Figure 28 RCU O ption Dialog B ox
The Minimum Paths op tion allows you to specify the minimum num b er of paths required for each
RCU connected to the current MCU (default = 1). If you enter a larger number 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), a n error occurs. When an error occurs, the MCU suspends all affected 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 Continuous Access pairs which
contain critical da ta for disaster recovery, set the minimum number of paths to one, so that Continuous
Access operations continue even if there is only one path to an RCU. If you need high p erformance at
the
MCU, set the minimu m number of paths to two or more (up to eight per CU), depending on the
number of pairs managed by the MCU.
Note: When you have Continuous Access A synchronous pairs c onfigured on a Fibre Channel interface,
set
the same value for the Minimum Paths option for all RCUs.
Caution: If Continuous Access pairs are suspended because the number of paths has dropped below
this setting, the P-VOL fence level pair option (see “Changing Pair Options” on page 110) determines
whether the Continuous Access Synchronous P-VOLs are fenced (that is, reject all write operations).
The RI O 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
valuemust befrom10to100 seconds. Thedefault setting is15 seconds. Thissetting is availablefor
both Fibre Channel and serial interfaces. For further information on the MIH, see the Hitachi TrueCopy
for z/OS User’s Guide.
The RoundTripTime setting is used for Initial Copy operations. This setting gives a priority to a remote
I/O
for an update copy operation.
When an Initial Copy op eration is in progress, the copy pace is automatically adjusted based on the
value (the actual time required for the initial copy), which can be obtained by subtracting the speci fi ed
Round Trip time (obtained using the formula below) from the remote I/O response time. If the actual
time
required for the initial copy operation is large, it means that the workload of the update copy is
relatively high. Therefore, the copy pace of the initial copy will be slowed. When the time is relatively
small, the copy pace will speed up to the specified value. In this way, we can curb the influence of the
exclusivelineuse in theinitial copy operationonthe host performance.
Note: This option is available only for Continuous Access Synchronous p airs. For Continuous Access
Asyn chronous pairs, this option value is invalid.
Thedefault valueof Round Trip Time is 1 ms. You may specify 1 ms to 500 ms. You can use the following
formula to figure outthe RoundTripTime.
Rou
nd Trip time =
Round Trip Time between MCU-RCU x 2
(*)
+ Initial Copy response time (ms)
(*)
A data transfer between the MCU and RCU involves t wo response sequences in one com mand
issuance. Therefore, you need to double the Round Trip Time bet ween the MCU and RCU.
For
the Round Trip Time between the MCU and RCU, ask your carrier, or use a ping command and so on
to
measure the time. If you do not use lines a nd so on. b et ween the MCU and RCU, specify 1.
The Initial Copy response time is the response time required for multiple initial copy operations. You
can use the following formula to get the Initial Copy response time. To get the time, you should use the
Performing Continuous Access Configuration Operations
76