I have virtual appliance
and sometimes get warning "Warning Data Service Health Alarm"
What is it mean?
In the desktop client, can you navigate to Home > Administration > vCenter Service Status
You should see more detail on this screen. Please upload a screenshot for us to review.
I dont have this tab
What do you see under vCenter Solutions Manager?
But right now I dont have this warning...
If it comes back, check this tab, also solutions and health. You will see more detailed information on those alerts there.
I hope this helps but if not, post a reply and I'll take a further look.