Last week I published a blog article about new performance counters in vSphere 5.1 for monitoring Storage I/O Control (SIOC). Soon after publishing, I received a question about the siocActiveTimePercentage counter, which only ever showed 0% or 100% values.
There was an interesting question posted recently around how you could monitor Storage I/O Control activity. Basically, how would one know if SIOC had kicked in and was actively throttling I/O queues? Well, in vSphere 5.1, there are some new performance counters that can help you with that.
Storage I/O Control (SIOC) was initially introduced in vSphere 4.1 to provide I/O prioritization of virtual machines running on a cluster of ESXi hosts that had access to shared storage. It extended the familiar constructs of shares and limits, which existed for CPU and memory, to address storage utilization through a dynamic allocation of I/O queue slots across a cluster of ESXi servers. The purpose of SIOC is to address the ‘noisy neighbour’ problem, i.e. a low priority virtual machine impacting other higher priority virtual machines due to the nature of the application and its I/O running in that low…