Each of the non-primary replica members appears to be asking the primary every minute for a "listDatabases". Since each requests takes about 2 seconds, every minute or so, we'll see our members lag on sync, because of this.

While some performance issues were fixed in SERVER-17078, the overall problem of time to return has not. Obviously with more than 250,000 files in our wiredTiger directory, one might expect it would take a bit of time to count the sizes.

I would suggest creating a listDatabases (like) method that did not get file and index sizes. This would be used for whatever purposes the replicasets require, without creating the massive requests to the filesystem and delays in synchronization