HP StorageWorks XP Remote Web Console Software - Manual (Page 24)

within the user-specified offloading timer value, the RCU suspends all XP Continuous Access
Asynchronous pairs and resets the channel-command-retry condition to avoid hanging up the MCU.
Table 4 (page 24) describes the sidefile threshold values for XP Continuous Access Asynchronous
operations and write pending operations and describes the actions that occur when each threshold
is reached.
Table 4 Sidefile Thresholds
Action(s) Threshold(s) Operation
MCU reaches threshold: I/O delay starts.
If the sidefile threshold is set between 0 to
30%, the influence on the I/O delay is kept
low.
RCU reaches threshold: No action.
I/O Delay Start (threshold) = 30%.
The threshold can be adjusted (to the
desired value between 0 and 70% in 1%
increment) using the XP Continuous Access
software.
Specify a value not exceeding the value of
I/O Delay Increase, and Sidefile threshold
for the I/O Delay Start threshold.
XP Continuous
Access
Asynchronous
MCU reaches threshold: I/O delay
increases. If the sidefile threshold is set
between 0 to 30%, the influence on the I/O
delay is kept low.
RCU reaches threshold: No action.
I/O Delay Increase (threshold) = 40%.
The threshold can be adjusted (to the
desired value between 0 and 70% in 1%
increment) using the XP Continuous Access
software.
Specify a value within the range of the I/O
Delay Start threshold and the Sidefile
threshold for the I/O Delay Increase
threshold.
XP Continuous
Access
Asynchronous
MCU reaches threshold: I/O delay.
RCU reaches threshold (70%): command
retry to MCU.
Sidefile threshold = 50%.
Threshold of MCU can be adjusted using
the XP Continuous Access software (30, 40,
50, 60, 70%).
XP Continuous
Access
Asynchronous
Command retry. [write pending] / [avail cache - sidefile] =
70% Write Pending
Cache Residency Manager operations may decrease the total amount of cache available for XP
Continuous Access Asynchronous operations, but do not directly affect sidefile cache usage.
Available cache is defined as the amount of physical cache memory installed on the storage system
minus any cache reserved for the Cache Residency Manager feature.
If you do not want to control the inflow into a sidefile, specify the same value as the Pending Update
Data Rate for both the I/O Delay Start and I/O Delay Increase, and 0 seconds for the offloading
Timer.
For information on Compatible XRC and Concurrent Copy (CC) cache sidefile operations, see the
Hitachi TrueCopy™ for Mainframe User Guide: HP XP24000 Disk Array, HP XP20000 Disk Array.
Storage systems performing XP Continuous Access Asynchronous in combination with Compatible
XRC and/or CC must have sufficient cache installed to handle the increased sidefile activity.
XP Continuous Access Synchronous Consistency Group Operations
You may specify a consistency group for XP Continuous Access Synchronous pairs by creating XP
Continuous Access Synchronous pairs and executing the operations on them by using RAID
Manager. Moreover, you may specify a consistency group for XP Continuous Access Synchronous
pairs by creating TrueCopy for Mainframe synchronous pairs and executing the operations on
them using Business Continuity Manager. Once a consistency group for XP Continuous Access
Synchronous pairs is specified, issue commands for each consistency group and maintain the
consistency of the pairs in the same group.
24 About XP Continuous Access Operations