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

Inflow Control b y RCU. When the amount of RCU sidefile c ache reaches the user-specified threshold
(pending update data rate), the RCU responds with channel-command-retry requests to the RIO commands
which transfer the recordsets from the MCU. The only recordset accepted by the RCU is the recordset with
the
sequence number required to continue settling the pending recordsets. If the RCU is not able to settle
a
recordset within the user-specified offloading timer value, the RCU suspends all Continuous Access
Asynchronous pairs and resets the channel-command-retry condition to avoid han ging up the MCU.
Table 4 on page25shows thesidefile threshold values for Continuous Access Asynchronous operations
and
write pending o perations and describes the actions that occur when each threshold is reached.
Table 4 Sidefile Thresholds
Operation
Threshold(s)
Action(s)
Continuous
Access
Asynchronous
I/O D elay Start (threshold) = 30%.
Note: The threshold can be adjusted (to
the desired value between 0 and 70%
in 1% increment) using the 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.
MCU reaches threshold: I/O delay starts.
If the
sidefile threshold is set bet ween 0
to
30%, the influence on the I/O delay
is
kept low.
RCU reaches threshold: No action.
Continuous
Access
Asynchronous
I/O Delay Increase (threshold) = 40%.
Note: The threshold can be adjusted (to
the desired value between 0 and 70%
in 1% increment) using the 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.
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.
Continuous
Access
Asynchronous
Sidefile threshol
d=50%.
Note: The thresho
ld
can be ad justed using
the Continuous Access software (30, 40,
50, 60, 7 0%).
MCU reaches threshold: I/O delay.
RCU reaches threshold: command retry
to
MCU.
Write P ending
[write pending] / [avail cache - sidefile]
=70%
Command retry.
Note: Cache Residency Manager o perations may decrease the total amount of cache available for
Continuous Access Asynchronous operations, but do not directly affect sidefile cache usage. Available
cache is defined as the amount of physical cache m emory installed on the storage system minus any
cache reserved for the Cache Residency Manager feature.
Note: 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.
F or information on Concurrent Copy (CC) cache sidefile operations, see the Hitachi TrueCopy for
Mainframe User’s G uide. Storage systems performing Continuous Access Asynchronous in combination
with CC must have sufficient cache installed to h andle the increased sidefile activity.
Continuous Access Asynchronous Consistency Group
Operations
Continuous Access Asynchronous consistency groups enable update sequence consistency to be
maintained across a group of volumes. The P-VOLs and S-VOLs of the pairs in a consistency group must
be
located
within one p hysical MCU and one physical RCU (1-to-1 requirement) . The Continuous Access
consistency group operations include:
• Group options, and
• Group oper
ations.
XP24000ContinuousAccessSoftwareUserand ReferenceGuide
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