I have a 3 node replica set that's been online since mid december. Last Friday (Jan 24), we added a 4th node in our disaster recovery data center.
We used the automatic initial sync procedure as our data set is relatively small. No problems here, after a while it's status switched to secondary and rs.printSlaveReplicationInfo() tells me everyone is in sync with little lag.
A coworker asked me to confirm that the new node was up to date and my instinct was to compare the size of the data folders (dbPath).
The new node's dbPath is ~1.88GB, but the average size for the other nodes is ~3.7GB. Why is the new node's dbPath smaller?
The real question is, how do I figure out if a new node of the Replica Set is fully synced?