We have a Mongo node running and we want to add a secondary and an arbiter. Current node will be our Primary. All three are up and running and have the exact same configuration. When we try to run rs.initiate(), we get "local.oplog.rs is not empty on the initiating member. cannot initiate" error. There is data in the local.oplog.rs collection on the primary. It's most likely got there during our original attempt to stand up the replica set. At that time if brought out primary down to its knees and we stopped. Since then, we copied most of the current data to the secondary. We were expecting for the nodes to come up and then for the secondary to balance the deltas. Should we just delete the contents of "local.oplog.rs"? Can we just drop it?