> can I get it to check server b if server a fails rather than just keeping the setting?
No.
DNS doesn't care about the service you run on an IP. That you got Server b back afterwards is pot-luck, it rotates the responses (that's what Round Robin does).
If you want service awareness you need to do one of these:
1. Have something monitor the service and modify DNS records if it fails
2. Get a Hardware Load Balancer
3. Use some form of Clustering
Chris