Storage Input Output Control.
One of the major improvements in the upcoming vSphere 4.1 is certainly the new storage IO control. (SIOC). With SIOC activated you can define QoS prioritization for the I/O activity on a single host or a cluster of hosts. Activating SIOC on your datastore, you're able to prevent an individual VM “to steel” the IOPs destined for the other VMs residing on the same datastore as well.
With this cool video below, you'll see how it works and how you will be able to activate it. Very simple. There had been many posts already describing in depth the functionning. See it:
I like the way Eric explains the functionning on his blog:
When Storage IO Control on a datastore is enabled, ESX/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 IO resources in proportion to their shares and is set per virtual machine. The number can be adjusted for each based on need. Low priority VMs can limit IO bandwidth for high priority VMs and storage allocation should be in line with VM priorities.
I watched the video several times and I saw the release of vSphere was 4.1 with build number 246491… But as I saw on Virtualization.info the version is “currently numbered 4.1, but likely to change in 4.5 to align with the upcoming release of View 4.5”. So we might not see the vSphere 4.1 at all, since it is in BETA, and the number will go directly into 4.5 ? Wait and see..