Hi Surya,
are you seeing this alarm in the vSphere web client? If so, you can see further information about the health degradation by going to Administration > System Configuration > Services (you'll have to be logged in as Administrator). If you go to the "VMware vSphere Web Client" and "Data Service", you should be able to see the reason for this alarm in the "Health Message" portlet on the Summary page.
Regards,
Irina
