vSphere Storage I/O Control allows cluster-wide storage I/O prioritization, which allows better workload consolidation and helps reduce extra costs associated with over provisioning.
Storage I/O Control extends the constructs of shares and limits to handle storage I/O resources. You can control the amount of storage I/O that is allocated to virtual machines during periods of I/O congestion, which ensures that more important virtual machines get preference over less important virtual machines for I/O resource allocation.
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 datastore is considered to be congested and each virtual machine that accesses that datastore is allocated I/O resources in proportion to their shares. You set shares per virtual machine. You can adjust the number for each based on need.
Configuring Storage I/O Control is a two-step process:
Enable Storage I/O Control for the datastore.
Set the number of storage I/O shares and upper limit of I/O operations per second (IOPS) allowed for each virtual machine.
By default, all virtual machine shares are set to Normal (1000) with unlimited IOPS.
Storage I/O Control is enabled by default on Storage DRS-enabled datastore clusters.