ESXTOP VAAI counters

While working on the vSphere 6 ESXTOP quick Overview for Troubleshooting poster, I came across the VAAI counters that are available with ESXTOP.

Finally I did not include them to the poster, because I doubt that they are relevant for troubleshooting in most cases.

But maybe someone finds this information useful – so here is the information summarized in a short blog post:

To display the VAAI stats open ESXTOP and press “u” to show the disk devices.

Now press “f” to add or remove fields. In our case we want to display only the fields A (Device Name) and O (VAAI Stats):


ESXTOP will now show you the following VAAI stats:


  • CLONE_RD – number of successfully completed CLONE commands where disk device was a source
  • CLONE_WR – number of successfully completed CLONE commands where disk device was a destination
  • CLONE_F – number of failed CLONE commands
  • MBC_RD/s – CLONE data read per second (in MB)
  • MBC_WR/s – CLONE data written per second (in MB)

CLONE_F  shows failed VAAI commands and should be zero. CLONE_F > 0 implies that there is/was a constraint on the array. In this case ESX will fail back to a software copy.

  • ATS – number of successfully completed ATS (Atomic Test & Set) commands
  • ATSF – number of failed ATS commands

If you see ATSF values > 0 it is not a problem in the short run. It only means that ESX falls back to SCSI-2 reservations for metadata updates for any reason. If you see SCSI reservation conflicts in a high number in the /var/log/vmkernel log you should give them a look.

  • ZERO – number of successfully completed ZERO commands
  • ZERO_F – number of failed ZERO commands
  • MBZERO/s – data zeroed per second (in MB)
  • DELETE – number of sucessfully completed DELETE commands
  • DELETE_F – number of failed DELETE commands
  • MBDEL/s – data deleted per second (in MB)

You are looking for more information about ESXTOP counters? You are looking for a description of the ESXTOP counters and thresholds?

Take a look at the ESXTOP Troubleshooting poster for vSphere 6. Or  better – print it and hang it on your office wall:

ESXTOP vSphere 6


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