Storage I/O Control

A new feature that was released with 4.1 is the VMware Storage I/O Control (SIOC). This feature allows for prioritizing access to your storage resources based on a predetermined policy. When set-up this will prevent cases of a single non critical VM taking hostage of your host for example. As well, it will allow for more virtualized apps because you can cram a whole bunch of low I/O VM’s without the fear of bottle necks. An added bonus is it will give the administrator some better predictability and you can dynamically allocate recourses as your needs change, plus since it is automatic you won’t need to manually manage for performance.

How it works and some limitations:

I/O control programmed on the datastore and is based on congestion policies. So once it detects latency it will then throttle back or forward for that datastore based on what you have told it to do.

A thing to note is that is designed to be a gradual enforcement and will not immediately scale down a machine. It is more of a guideline to help with the performance SLA’s for your VM’s.  It is only supported on Fibre Channel and iSCSI and if you have datastores with multiple extents or NFS datastores it won’t be supported.

To Enable Storage I/O Control:

  1. Select a datastore in the vSphere Client inventory and click the Configuration tab.
  2. Click Properties.
  3. Under Storage I/O Control, select Enabled.
  4. Click Close.

Some Details:

By default, all virtual machines have the same number of shares and IOPs limit.

  • By default, IOPs are unlimited.
  • Even if you enable this feature, if you don’t change the defaults, I/O won’t prioritize any VM’s, not very useful.
  • Lastly, to make sure everything is working well, it would be recommended to turn on logging:

To enable logging:

  1. Click Host Advanced Settings.
  2. In the Misc section, select the Misc.SIOControlLogLevel parameter. Set the value to 7 for complete logging. For example:Min value: 0 (no logging)
    Max value: 7
  3. Perform the action that is failing or repeat the procedure to replicate the observed issue.

Check out the video below:


Leave a Reply

Your email address will not be published. Required fields are marked *

You may use these HTML tags and attributes: <a href="" title=""> <abbr title=""> <acronym title=""> <b> <blockquote cite=""> <cite> <code> <del datetime=""> <em> <i> <q cite=""> <s> <strike> <strong>