How do i find my storage supports VAAI?

I don't think VAAI is supported in AX4-5 array. You can look at EMC CLARiiON Integration with VMware ESX, it listed CX4 and AX4 arrays but said CX4 is only supported array for VAAI on page 56.

not supported I'm afraid. AX4-5 is only certified for use up to Flare 23.

http://www.vmware.com/resources/compatibility/detail.php?deviceCategory=san&productid=3359&releaseid=76&deviceCategory=san&partner=30&keyword=AX4&isSVA=1&page=1&display_interval=10&sortColumn=Partner&sortOrder=Asc

In general, the easiest way to check whether a particular storage product supports VAAI is:

1. Go to the VMware Compatibility Guide - http://www.vmware.com/resources/compatibility/search.php
2. Under "What are you looking for", select "Storage/SAN"
3. Under "Product Release Version", select your version of vSphere
4. Under "Partner Name", select the storage vendor you're interested in
5. Under "Features Category", choose one of "VAAI-Block" or "VAAI-NAS", depending on what you're looking for
6. Click "Update and View Results"

This will give you the definitive answer from VMware's point of view.