Signs That your disk usage is too high

Whether you are converting physical to virtual, creation of new machines, or existing virtual machines are using additional resources then originally specified two years ago; at sometime your environment will run out of resources. Most of the time you will run out of disk or memory.

When it comes to running out of disk, you could run out of actual space or the number of IOPS (Input Outputs Per Second). Most SANs and even VMware is very good at showing space utilization, but to show that you are suffering issues from maxing out the I/O is not as easily understood.

First lets look at the GUI, you can go to a specific virtual machine and click on the performance tab.  Click the Advanced button.  Under the Switch To drop-down box, select Disk.  Then click on Chart Options, then select Command Aborts. Click OK.  As you can see in my example we are at zero which is good, if this virtual machine was registering anything.  If you have anything other then zeroes, then you I/O pipe is bottlenecked somewhere and the storage is issuing a SCSI command abort.

NewImage

I prefer to do it by the virtual machine, but you can also do it by selecting the host and going through the same steps.  The difference is that the Virtual Machine view will give you only the LUNS that are connected to that virtual machine, where in Host view it will give you all the LUNs connected to the host.

The next method I prefer to use as I think it is not only faster but more accurate; and that is using the command line and ESXTOP.  From the either local tech support or remote tech support command line enter ESXTOP, I prefer removing in via SSH so that you can expand the screen.  Once in ESXTOP, press the d key on the keyboard, this will bring you to the disk view and show you all list disk controllers.  The counters you want to look at specifically are:

  • DAVG/cmd
  • KAVG/cmd

ESXTOP1

DAVG/cmd should not be over 25, this usually means that there is an issue on the array causing the latency.  KAVG/cmd should never be over 2, if it is there is an issue with the host that is causing the latency.  This could be that the is a virtual machine with a high amount of I/O load (SQL or Exchange) that could be causing the issue.  To find out hit the v key on the keyboard to breakout the disk usage by virtual machine.  To break it out LUN you can press the u key.  This way you can figure out the culprit or culprits and take steps to fix the issue and bring the environment back to normal.

 

 

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