Now that we have lock + fsync we can take clean file system snapshots.
Given a snapshot of a master (or a slave) we should be able to create a new slave very quickly.

Process for ec2
1) lock + fsync
2) ebs snapshot
3) mount snapshot on the new slave
4) start slave with normal paramets
5) should know its "new" b/c setup as master, then take the newest value in the oplog and put that in local.sources

even not on ec2 this should be faster because you can compress the entire data set and don't have to re-create indexes