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Storage I/O Control (SIOC) is a VMware capability that allows cluster-wide storage I/O prioritization. Storage I/O Control extends the constructs of shares and limits to handle storage I/O resources – in other words I/O DRS. The I/O control is enabled on the datastore, and the prioritization is set at the virtual machine (VM) level. VMware claims that this method enables better workload consolidation and helps reduce extra costs that are associated with over-provisioning. The idea is that you can take many different applications, with disparate I/O requirements, and store them on the same datastore.
If the datastore (the underlying LUN) begins to provide degraded I/O response, VMware automatically adjusts the I/O share on a VM based on user-defined levels. This adjustment 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 you enable 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 (the default is 30 milliseconds), the datastore is considered to be congested. Each virtual machine that accesses that datastore is allocated I/O 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 118 illustrates how the datastore entitled CONCURRENT_DS_1 is enabled for Storage I/O Control. Right-click the datastore in question and select Configure Storage I/O Control. A dialog box appears which by default shows that the feature is 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 Technologies does not recommend using statistics with SDRS, the box is cleared in the example below. Even if it is enabled, the statistics are irrelevant if statistics are disabled when using SDRS.
The configuration change shows up as a Recent Task and once complete the Configure -> General page lists the feature as enabled as seen in Figure 119.
The second step in the setup of Storage I/O Control is to allocate:
When storage I/O congestion is detected for a datastore, the I/O workloads of the virtual machines accessing that datastore are adjusted according to the proportion of virtual machine shares each VM has been allocated.