6.0

On the Datastores tab, the Storage I/O Control column shows that Storage I/O Control is enabled for the
datastore.
Set Storage I/O Control Threshold Value
The congestion threshold value for a datastore is the upper limit of latency that is allowed for a datastore
before Storage I/O Control begins to assign importance to the virtual machine workloads according to their
shares.
You do not need to adjust the threshold setting in most environments.
CAUTION Storage I/O Control will not function correctly unless all datatores that share the same spindles on
the array have the same congestion threshold.
If you change the congestion threshold setting, set the value based on the following considerations.
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A higher value typically results in higher aggregate throughput and weaker isolation. Throttling will
not occur unless the overall average latency is higher than the threshold.
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If throughput is more critical than latency, do not set the value too low. For example, for Fibre Channel
disks, a value below 20 ms could lower peak disk throughput. A very high value (above 50 ms) might
allow very high latency without any significant gain in overall throughput.
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A lower value will result in lower device latency and stronger virtual machine I/O performance
isolation. Stronger isolation means that the shares controls are enforced more often. Lower device
latency translates into lower I/O latency for the virtual machines with the highest shares, at the cost of
higher I/O latency experienced by the virtual machines with fewer shares.
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If latency is more important, a very low value (lower than 20 ms) will result in lower device latency and
better isolation among I/Os at the potential cost of a decrease in aggregate datastore throughput.
Prerequisites
Launch the vSphere Client and log in to a vCenter Server system.
Verify that Storage I/O Control is enabled.
Procedure
1 In the vSphere Client inventory, select a datastore and click the Configuration tab.
2 Click Properties.
3 Under Storage I/O Control, select the Enabled check box.
4 (Optional) Click Advanced to edit the congestion threshold value for the datastore.
The value must be between 10 ms and 100 ms.
5 (Optional) Click Reset to restore the congestion threshold setting to the default value (30 ms).
6 Click OK and click Close.
Managing Resource Pools
A resource pool is a logical abstraction for flexible management of resources. Resource pools can be grouped
into hierarchies and used to hierarchically partition available CPU and memory resources.
Each standalone host and each DRS cluster has an (invisible) root resource pool that groups the resources of
that host or cluster. The root resource pool does not appear because the resources of the host (or cluster) and
the root resource pool are always the same.
vSphere Administration with the vSphere Client
352 VMware, Inc.