Inflow Control By Mcu; Inflow Control By Rcu; Continuous Access Xp Asynchronous Consistency Group Operations; Group Options - HP xp12000 User Manual

threshold (I/O delay increase), the disk array's I/O delay starts increasing. If the MCU cannot send a
recordset to the RCU within the user-specified offloading timer value because the amount of MCU sidefile
cache exceeded the sidefile threshold continuously, the MCU suspends all affected Continuous Access XP
Async volume pairs and resets the SCP condition to avoid hanging up the system.

Inflow control by RCU

When the amount of RCU sidefile cache reaches the user-specified threshold, the RCU responds with
channel-command-retry requests to the RIO commands that transfer recordsets from the MCU. The RCU
accepts only the recordset with the sequence number required to continue settling pending recordsets. If
the RCU cannot settle a recordset within the user-specified offloading timer value, the RCU suspends all
Continuous Access XP Asynchronous volume pairs and resets the channel-command-retry condition to
avoid hanging up the MCU.
Table 5 shows sidefile threshold values for Continuous Access XP Asynchronous operations and write
pending operations and describes actions occurring when each threshold is reached.
Table 5 Sidefile threshold values for Continuous Access XP Asynchronous operations and write pending
operations
Operation
Continuous Access
XP
Asynchronous
Continuous Access
XP
Asynchronous
Continuous Access
XP
Asynchronous
Write Pending
HP Cache LUN XP operations might decrease total amount of cache available for Continuous Access XP
Asynchronous operations, but they do not directly affect sidefile cache usage. Available cache is the
amount of physical cache memory installed on the disk array minus any cache reserved for the HP Cache
LUN XP feature.
If you do not want to control inflow into a sidefile, specify the value of the Pending Update Data Rate for
the I/O Delay Start and I/O Delay Increase, and specify 0 seconds for the Offloading Timer.

Continuous Access XP Asynchronous consistency group operations

Continuous Access XP Asynchronous consistency groups maintain update sequence consistency across an
aggregated data set spanning a group of volumes. P-VOLs and S-VOLs of the pairs in a consistency group
must be located within one physical MCU and one physical RCU (1-to-1 requirement). Continuous Access
XP consistency group operations include:
•

Group options

• Group consistency time
• Group operations
Group options
Continuous Access XP provides the following options for each consistency group: copy pending timeout
and RCU ready timeout. These options are selected when you add a group, and can be modified only
when the group does not contain any P-VOLs in the MCU.
Thresholds
I/O Delay Start (threshold) = 30%
Continuous Access XP
Use
desired value between 0 and 70% in 1%
increments. Specify a value not exceeding the value
of I/O Delay Increase, and Sidefile threshold.
I/O Delay Increase (threshold) = 40%
Continuous Access XP
Use
desired value between 0 and 70% in 1%
increments. Specify a value within the range of the
I/O Delay Start threshold and Sidefile threshold.
Sidefile threshold = 50%
Continuous Access XP
Use
(30, 40, 50, 60, or 70%).
[write pending] / [avail cache - sidefile] = 70%
Continuous Access XP user guide for the XP12000/XP10000
Actions
MCU reaches threshold: I/O delay
starts. If sidefile threshold is set
to adjust threshold to
between 0 and 30%, influence to
the I/O delay is kept low.
RCU reaches threshold: No action.
MCU reaches threshold: I/O delay
increases. If sidefile threshold is set
to adjust threshold to
between 0 and 30%, influence to
the I/O delay is kept low.
RCU reaches threshold: No action.
MCU reaches threshold: I/O delay.
RCU reaches threshold: Command
to adjust threshold
retry to MCU.
Command retry.
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