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Storage I/O Control (SIOC) is a VMware capability that allows cluster-wide storage IO prioritization. Storage I/O Control extends the constructs of shares and limits to handle storage IO resources – in other words IO DRS. The IO control is enabled on the datastore and the prioritization is set at the virtual machine (VM) level. VMware claims that this allows better workload consolidation and helps reduce extra costs associated with over-provisioning. The idea is that you can take many different applications, with disparate IO requirements, and store them on the same datastore.
If the datastore (that is the underlying LUN) begins to provide degraded performance in terms of IO response, VMware will automatically adjust a VM’s IO share based upon user-defined levels. This ensures that those VMs running more important applications on a particular datastore get preference over VMs that run less critical applications against that datastore.
When one enables Storage I/O Control on a datastore, ESXi begins to monitor the device latency that hosts observe when communicating with that datastore. When device latency exceeds a threshold (currently defaults to 30 milliseconds), the datastore is considered to be congested and each virtual machine that accesses that datastore is allocated IO resources in proportion to their shares as assigned by the VMware administrator.
Note: Storage I/O Control is fully supported with service levels.
Configuring SIOC is a two-step process as it is disabled by default:
The first step is to enable SIOC on the datastore. Figure 133 illustrates how the datastore entitled CONCURRENT_DS_1 is enabled for Storage I/O Control. Right-click on the datastore in question and select Configure Storage I/O Control. A dialog box appears which by default will
have the feature disabled. There are two main options available as the current disabled state is default from datastore creation. The first is to enable SIOC with or without statistics, and the second is to disable SIOC but enable statistics with SDRS. In this example, SIOC is enabled by selecting the first option. By default, the option to include I/O statistics for SDRS is enabled, however, as Dell does not recommend using statistics with SDRS, the box is unchecked in the example below. Note that even if it is enabled, as long as statistics are disabled when using SDRS, the statistics are irrelevant.
The configuration change will show up as a Recent Task and once complete the Configure -> General page will list the feature as enabled as seen in Figure 134.