I have a replicaSet with 2 database nodes and 1 arbitor.

All db are running fine for a long time at my customer site. One day, the primary db was brought down for maintenance. After about 2 hours, the-was-primary was brought back up, and becomes primary again, and secondary db is in Rollback state.

I have a few questions regarding above mentioned scenarios:

• when the primary db was brought down the first time, if there are db entries haven't synced to the secondary db, what would happen?
• when the failed primary brought back up again, does it become primary right the way? Does it sync with now-primary-was-secondary db before becoming primary db again?
• how do I recover the lost data in rollback folder given my latest primary and secondary db state?

Thanks and regards.