Hello,
If you want to configure alarms latency datastore, you must fastidiously to third party tools to do so from the vsphere. But if you can set alarms for each LUN (datastore) from the storage array.
For best performance, look at this KB where it indicates how to calculate IOPS.
And if you want to do everything from vcenter, set alarms VM.
For more information look at you this BOOK on page 19 "Char Analysis".