Web server session Persitence

We have load balanced JDE Web servers on IBM Websphere 7.0 on E1 9.0 TR 9.1.4.4. During testing I found that the user would be kicked out if server he is working goes offline. I am evaluating options to manage session persistence to prevent user from loosing his session and is moved to active server if one goes offline.
Can you share your experience on best methods for session persistence on Websphere and experience/feedback?.

Thanks,
Chan