VMware Storage Filters

VMware Storage Filters

This might not be a new thing but I had a thought of writing an article regarding these filters while I was studying in my VCAP exams. I have tested these things in my test lab and I think it is good thing to write an article with my own experience.

There are four main storage filters in VMware:

  1. VMFS Filter
  2. RDM Filter
  3. Same Host and Transports Filter
  4. Host Rescan Filter

By default these filters are enabled and you can manually edit these filters under vCenter server settings.

Before that I would like to explain the main purpose and requirement of these filters along with the associate parameters which you can change manually and enable the functionalities.

  • VMFS Filter

 Associate Parameter : config.vpxd.filter.vmfsFilter

This filter prevents you from adding a LUN which is already using by a different datastore. this parameter value is set to “true” by default and you can manually set this to false and enable to add any VMFS volume which is currently using by a different datastore. Obviously, there is a risk of data corruption and does not recommend to change these values unless you have a special requirement.


  • RDM Filter

Associate Parameter : config.vpxd.filter.rdmFilter

This filter prevents you from adding a RDM LUN to a Virtual Machine which is already using by a different Virtual Machine. Manually setting this filter to false and adding to a Virtual Machine can be a data loss or corruption of the original Virtual Machine.


  • Same Host and Transports Filter

Associate Parameter : config.vpxd.filter.SameHostAndTransportsFilter

This Storage filter prevents you from creating a datastore extent from an incompatible LUN.


  • Host Rescan Filter

Associate Parameter : config.vpxd.filter.hostRescanFilter
This is the only filter normally use in the production environment and this filter enables automatic rescan and update your Hosts after you adding a new VMFS datastore. This filter can be used when you are adding multiple datastore and you don’t need to rescan your Hosts each and every time.

How can we change these filters?

Yes, the next question would be “How can we change these Parameters?”, these parameters are defined under the vCenter settings.
  • Go to your Home page in the vSphere Management console and select “vCenter Server Settings” or  select “Administration” and “vCenter Server Settings”
  • Select “Advanced Settings” to view avialble parameters, as I said these parameters are set to “true” and not visible by default

Example of changing the Filters

Here what I’m going to show is changing the RDM Filter and add an existing LUN to a VM. Performing this task in a Production Environment can leads to a data loss or corruption

I have a VM (XPVM_01) with RDM LUN attached and it does not allow to attach the Existing LUN to a different VM (XPVM_02), by default if there are now free RDM LUNs available the “RAW Device Mapping” option is grayed out

Feature is grayed out since there is no free LUN in my SAN

Now I’m going to set the “config.vpxd.filter.rdmFilter” with the value of “false”, click on “Add” to add the parameter

Once you add the parameter you can see it and click “OK” to continue

Now I’m able to add the existing RDM LUN which is mapped to my “XPVM_01” VM to the second VM which is XPVM_02.

Once you add this filters in to the advanced settings of your vCenter you can go back and change the values to “true” and it is visible in the list.

You can read more on Storage Filters from this VMware KB reference.

I hope you enjoyed my post and thank you for viewing ……

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