Thursday, May 1, 2014

SIOC - VMware vSphere Storage I/O Control - Enhancement

Today I plan to write about the enhancements in Storage I/O control in vSphere 5.1 platform. Those of you who need some heads up can read about SIOC in my previous blog post here

The following are the new enhancements to Storage I/O Control in vSphere 5.1.

1. Stats Only Mode

SIOC is now turned on in stats only mode automatically. It doesn't enforce throttling but gathers statistics to assist Storage DRS. Storage DRS now has statistics in advance for new datastores being added to the datastore cluster & can get up to speed on the datastores profile/capabilities much quicker than before.

2. Automatic Threshold Computation

The default latency threshold for SIOC is 30 msecs. Not all storage devices are created equal so this default is set to a middle-of-the-ground range. There are certain devices which will hit their natural contention point earlier than others, e.g. SSDs, in which case the threshold should be lowered by the user. However, manually determining the correct latency can be difficult for users. This motivates the need for the latency threshold to get automatically determined at a correct level for each device. Another enhancement to SIOC is that SIOC is now turned on in stats only mode. This means that interesting statistics which are only presented when SIOC is enabled will now be available immediately.

To figure out the best threshold, the new automatic threshold detection uses the I/O injector modelling functionality of SIOC to determine what the peak throughput of a datastore is.

When peak throughput is measured, latency is also measured.

The latency threshold value at which Storage I/O Control will kick in is then set to 90% of this peak value (by default).

vSphere administrators can change this 90% to another percentage value or they can still input a millisecond value if they so wish.

3. VMobservedLatency

VmObservedLatency is a new metric. It replaces the datastore latency metric which was used in previous versions of SIOC. This new metric measures the time between VMkernel receiving the I/O from the VM, and the response coming back from the datastore. Previously we only measured the latency once the I/O had left the ESXi host, so now we are also measuring latency in the VMkernel as well. This new metric will be visible in the vSphere UI Performance Charts.

PS :  All the disk operations on VM like backup, Storage vMotion etc are billed to SIOC. 

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