DSA (Datastore Alert)
"DSA" is a Windows service that will alert a list of recipients, if any of your datastores drop below a specified percentage.

Scenario: Out of now where your thinned provisioned servers starts to saturate your datastore. You configured DSA to notify you when space drops below 10% and you receive an email that your VMFS just dropped below that 10% mark. You login to Vcenter and start migrating your data to another datastore. You then decided to extend your volume within your EQL SAN and continue to extend the VMFS within Vcenter. After rescanning you datastores DSA sends another alert saying the space issue has been cleared.

DSA can also be configured to use Push requests for applications like C-OUT. This CTI application for Cisco CUCM will call you and playback an alert message. "Warning your VMFS is below it's space threshold". or another other WAV file you like.