Continuous Access Xp Asynchronous Consistency Group Operations; Group Options; Sidefile Thresh. Vals. For C Xp Asynch. Ops. And Write Pending Ops - HP StorageWorks XP12000 User Manual

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 6 shows sidefile threshold values for Continuous Access XP Asynchronous operations and write
pending operations and describes actions occurring when each threshold is reached.
Table 6 Sidefile thresh. vals. for C XP Asynch. ops. and write pending ops.
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.
26
Continuous Access XP for the Array
Thresholds
I/O Delay Start (threshold) = 30%
Use Continuous Access XP to adjust
threshold to 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%
Use Continuous Access XP to adjust
threshold to 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%
Use Continuous Access XP to adjust
threshold (30, 40, 50, 60, or 70%).
[write pending] / [avail cache -
sidefile] = 70%
Actions
MCU reaches threshold: I/O delay
starts. If sidefile threshold is set
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
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
retry to MCU.
Command retry.