SIOC was initially introduced in vSphere 4.1 to provide I/O prioritization and quality of service (QoS) of VM disks running on a cluster with a shared storage. It extended the shares and limits not at the host level, but at the cluster level. With vSphere 5.0, SIOC provides cluster-wide I/O shares and limits for NFS datastores, not only VMFS datastores.

With vSphere 5.1 a new SIOC feature called stats only mode is used to gather statistics to assist SDRS. Also, the latency threshold for SIOC has a new automatic threshold computation and the default latency threshold for SIOC (30 ms) can be reduced to as low as 5 ms.

With vSphere 6.5 there are two different SIOC:

• SIOC V1: It is disabled by default. It needs to be enabled on per datastore level, and it is only utilized when a specific level of latency has been reached. By default, the latency threshold for a datastore is set to 30 ms, as mentioned earlier. If SIOC is triggered, disk shares (aggregated from all VMDKs using the datastore) are used to assign I/O queue slots on a per-host basis to that datastore. In other words, SIOC limits the number of IOs that a host can issue. The more VMs/VMDKs that run on a particular host, the higher the number of shares, and thus the higher the number of IOs that particular host can issue. The throttling is done by modifying the device queue depth of the various hosts sharing the datastore. When the period of contention passes, and latency returns to normal values, the device queue depths are allowed to return to their default values on each host.
• SIOC V2: This can now be managed using Storage Policy Based Management (SPBM) policies. VM Storage Policies in vSphere 6.5 have a new option called common rules, used for configuring data services provided by hosts, such as SIOC and encryption.

To build a new SIOC storage policy, the first step is to enable common rules. This will then allow you to add SIOC components to the policy:

Note that, actually, building a new VM storage policy is possible only from the vSphere Web Client. Assigning it to a VM is possible also from the HTML5 client.