July 15, 2015

Storage I/O Control (SIOC)

SIOC

VMware vSphere Storage I/O Control (SIOC) provides I/O prioritization of virtual machines running on a cluster of ESXi hosts with access to shared storage. It extends the constructs of shares and limits, which existed for CPU and memory, to manage storage utilization.

Use SIOC to configure rules and policies to specify the business priority of each virtual machine using shares and limits. When I/O congestion is detected, Storage I/O Control dynamically allocates the available I/O resources to virtual machines according to the rules and policies, improving service levels and consolidation ratios.

At a basic level SIOC is monitoring the end to end latency of a datastore. When there is congestion, SIOC reduces the latency by throttling back virtual machines that are using excessive I/O. SIOC will use the share values assigned to the virtual machine’s VMDKs to prioritize access to the datastore.

The purpose of SIOC is to address the noisy neighbor problem, i.e. a low priority virtual machine impacting other higher priority virtual machines due to the nature of the application and the I/O characteristics of the low priority VM.

SIOC allows vSphere administrators to assign relative priority to storage I/O as well as assign storage I/O limits to VMs.

Once enabled for a specific datastore, SIOC will monitor the datastore, summing up the disk shares for each of its VMDK files. When an ESXi host detects storage congestion through an increase of latency beyond a user-configured threshold, it will apply the settings configured for that VM.


SIOC resolves imbalances by limiting the amount of I/O operations a host can issue for a datastore. The result is that VMware administrators can ensure that VMs that need priority access to storage resources get the resources they need.

Storage I/O Control (SIOC) requires Enterprise Plus licensing..

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