Using Execution Throttles; Calculating Execution Throttles; Examples - HP Open View Installation And Maintenance Manual

Configuring Hosts and Storage Arrays

Using execution throttles

This section describes how to calculate the execution throttle for an HBA driver and lists the
procedures to set the execution throttle for specific HBA drivers:

Calculating execution throttles

Execution throttles enable you to balance the workload on the appliance. The execution
throttle value determines the maximum input/output (I/O) allowed on each node target port. It
also determines the maximum number of I/O commands allowed from the host HBA
simultaneously.
When HP Manufacturing installs the appliance software, the execution throttle value for the
node target ports is set automatically. However, you must set the execution throttle value for
each host HBA that is connected to the appliance.
The appliance has the following execution throttle limits:
Do not exceed either limit when calculating the execution throttle for each host HBA; it can
cause the appliance to return SCSI_QUEUE_FULL frames to the hosts, resulting in retries or
I/O failures on the host. HP strongly recommends that you follow these execution throttle
guidelines for all installations.

Examples

If three hosts are directly connected to the appliance, set the execution throttle value to 480 for
each host. Because there are three unused target ports on each node, you will not exceed the
execution throttle limit.
If five hosts are connected through a switch, they can use any of the node's target ports for I/O.
Therefore, you divide 480 by the number of hosts (in this case, 5). Use the result, 96, as the
execution throttle value for each host.
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Calculating execution throttles
Setting the execution throttle for QLogic HBAs
Setting the execution throttle for Emulex HBAs
The maximum queue depth for each node is 2000.
The maximum queue depth for each node target port is 480.
Continuous Access Storage Appliance Installation and Maintenance Guide