Thin provisioned custom alarm trigger

Hi,

I am trying to understand when "Thin-provisioned volume capacity threshold exceeded" custom alarm in Vcenter 6.x would get triggered.

I have a datastore backed by iSCSI based LUN and the storage supports thin provisioning. After crossing the set soft threshold ,I could see the event "Space utilization on thin provisioned device naa.XX exceeded configured threshold" on ESX/Vcenter but the custom alarm is not triggered.

Any pointers to how to trigger this alarm would be helpful.

Is VAAI support mandatory to trigger this alarm on Vcenter? Is there any documenation/KB article from VMWare stating this?

Thanks!