Let's Virtualize: Storage I/O Control

SIOC is a method to ensure that the VM's on datastore get a fair share of I/O resources during the period of high contention or latency.
Important Virtual Machines get preferences when compared to less important Virtual Machines for I/O resource allocation.
Can be used both with and without Storage DRS as it includes two different thresholds i.e Standalone without DRS and with vSphere Storage DRS.
SIOC is aware about the average latency, active VM's and also the priorities associated with them.
Quite Similar to the concept used by DRS for CPU/Memory the higher the shares value higher the resources it get.
vCenter is only used for enabling and disabling the feature and for changing the thresholds.

SIOC is supported on FC,ISCSI, and NFS not supported with Raw Device Mapping (RDM)
vSphere Enterprise Plus License.
Datastore which are SIOC enabled must be managed by single vCenter Server.

To configure the vSphere SIOC enable it for the particular datastore as it is disabled by default.
Set the number of storage I/O shares for each VM's and limit for IOPS by default the limit is unlimited.
Once Enabled ESXi starts monitoring the latency when communicating with the datastore and if it exceeds the threshold value means it's congested.
SIOC uses Workload Injector Based Model and only runs when the datastore is in an ideal state.
It automatically determines the latency, moreover this can also be overridden by specifying specific latency value.
Automatic detection works well when you have multiple disk arrays and many datastore are configured for SIOC.