Server Fault is a question and answer site for system and network administrators. It's 100% free, no registration required.

Sign up
Here's how it works:
  1. Anybody can ask a question
  2. Anybody can answer
  3. The best answers are voted up and rise to the top

I have a rather unusual predicament. Data centre provided SAN as a service which sounded good at the time :(. I am running ESX 4.1 across multiple hosts. I am getting alerted quite regularly about "An external I/O activity is detected on datastore “*”".

My understanding of this is (simply) that my hosts have throttled IO to identify if problem goes away, it does not so it raises alert.

My question is should SIOC be enabled in a situation where you have a shared SAN and do not know who else is using it and what they are running on it?

share|improve this question

Yes and no.

You can increase the thresholds before SOIC will be active or other wise you will need to disable it.

I recently had the pleasure of meeting Duncan Epping (Tech architect at VMware for SOIC). He has an excellent blog post on SOIC here and there is a known KB about this here

I would have a read of these and this should give you the information to be able to decide if you should or shouldn’t disable SOIC.

An Extract from the KB shows the No part of my Yes and No.

"Note: SIOC can be used even when External Workloads are using the same underlying storage array as vSphere. This could be detrimental to the I/O performance of the virtual machines. To function in presence of external workloads, SIOC needs to throttle virtual workloads; around 10% average if the external workload interference is continuous. If this is not acceptable, currently, disabling SIOC is the only solution. But, if the external workload is temporal, for example, for a few hours and there is sufficient capacity on the array, enabling SIOC acts as an insurance against IO performance problems that may happen due to mis-configurations in a shared storage virtual environment. "

share|improve this answer

Your Answer


By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.