Is a Virtual Machine Bringing Your Storage Down?


Have you ever had a user running IOmeter on a virtual machine just to ‘test’ the performance of the virtual disk… at 9am…on a Monday morning??

Well it might happen to you once but not twice as you would immediately have powered off the virtual machine and eventually head shoot the useršŸ™‚

There is a more elegant way to mitigate the risk of having a valid virtual machine though but still able to put down your storage on its knee and ruining your Monday morning.

  • Power off the virtual machine
  • Click Edit Settings.
  • Click theĀ OptionsĀ tab.
  • Under theĀ Advanced: GeneralĀ section, click theĀ Configuration ParametersĀ button.
  • Click theĀ Add RowĀ button.
  • Add one or both of these settings for each virtual disk device:

sched. < diskname > .throughputCap = < value >< unit >

For example: sched.scsi0:0.throughputCap = 10KIOps

sched. < diskname > .bandwidthCap = < value >< unit >

For example:Ā sched.scsi0:0.bandwidthCap = 10KBps

TheĀ <value>Ā is eitherĀ offĀ or an integer, andĀ is a string beginning withĀ KĀ (KBpsĀ orĀ KIOps),Ā MĀ (MBpsĀ orĀ MIOps) orĀ G(GBpsĀ orĀ GIOps). If no units are specified, the default ofĀ KĀ is assumed.

[UPDATE] You can cap below the k (thousand) by omitting K, M or G. e.g. 100IOps will cap at maximum 100 IO per second.

  • Start the virtual machine. The virtual machine I/O is limited to the specified values.

This is only available in vSphere 4.1
Source: VMware KBĀ 1038241

About PiroNet

Didier Pironet is an independent blogger and freelancer with +15 years of IT industry experience. Didier is also a former VMware inc. employee where he specialised in Datacenter and Cloud Infrastructure products as well as Infrastructure, Operations and IT Business Management products. Didier is passionate about technologies and he is found to be a creative and a visionary thinker, expressing with passion and excitement, hopefully inspiring and enrolling people to innovation and change.
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8 Responses to Is a Virtual Machine Bringing Your Storage Down?

  1. So what would the value need to be? How would you calculate this?

    I would suggest just enabling SIOC and use “IOps limits” on disk.

    • deinoscloud says:

      Hi Duncan and thx for your comment,

      How to calculate the value? Well it depends :))

      SIOC is premium and not all customers can afford itšŸ˜¦

      When you set the ‘Limit IOPS’ you actually set the sched.scsi0:0.throughputCap if I’m not wrong…

      Now with SIOC turned on, I’m not sure if the Limit IOPS is enforced or does it kick in when SIOC gradually enforce the predefined I/O share levels only… What’s your take on this?

  2. hussain says:

    hi, it happened to me once when i was testing veeam on iscsi server running starwind. Not the ST server went down but the ESX Server hangs and the veeam vm and the target machine hang and no response at all. My only option it to kill the host and start it back along with the vms were running on it.

    Root cause of this issue is Jumbo frame is not configured0 on the switch, vmkernel and messeges logs with full of iscsi errors and disconnection to the target

  3. John says:

    Hi Didier,

    Thanks for sharing but I hope people don’t simply copy the values you supplied from the picture you added in this blog.

    I guess 10KIOPS as a value for “BandwidthCap” won’t work as expected, results with this funny ‘Monday morning IOMeter test’ with 10.000 IOPS, let’s say with a 512KB block size and a sequential 100% write to the SP won’t be that funny…..šŸ˜¦

    Personally I would stick with SIOC or tuning storage on the advanced/disk settings (queue depths & block sizes) on the host level.

    // John

    • deinoscloud says:

      Hi John,

      Thx for your comment.

      Indeed 10KIOps is already such a high value that many storage arrays out there would have already ran out of gasšŸ™‚

      I’ve tested with 200IOps (yes you can set IOps below the K level) and it works great…

      Read my next post on this matter cause I believe IMO there are cases where these parameters can be a good fit….

      Stay tunedšŸ™‚

  4. Pingback: Limiting Disk I/O From A Specific Virtual Machine | DeinosCloud

  5. g_mulholland says:

    How do I manage that across, lets say 50 VM’s, in a large environment. Micro Management techniques are not a workable solution as far as I am concerned. The fact that you don’t mention that it becomes a messy solution in such an environment worries me.

    • deinoscloud says:

      Hi and thx for your comment,
      You should just turn on SIOC if you have Ent+ license(s).
      Source of the article is a VMware KB where alternate options are proposed…

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