Mongodump with --oplog for hot backup

Question

I'm looking for the right way to do a Mongodb backup on a replica set (non-sharded).

By reading the Mongodb documentation, I understand that a "mongodump --oplog" should be enough, even on a replica (slave) server.

From the mongodb / mongodump documentation :

--oplog Use this option to ensure that mongodump creates a dump of the database that includes an oplog, to create a point-in-time snapshot of the state of a mongod instance. To restore to a specific point-in-time backup, use the output created with this option in conjunction with mongorestore --oplogReplay.

Without --oplog, if there are write operations during the dump operation, the dump will not reflect a single moment in time. Changes made to the database during the update process can affect the output of the backup

I'm still having a very hard time to understand how Mongodb can backup and keep writing on the database and make a consistent backup, even with --oplog. Should I lock my collections first or is it safe to run "mongodump --oplog ? Is there anything else I should know about?

Thanks.

Answer 1

The following document explains how mongodump with –oplog option works to create a point in time backup.

http://docs.mongodb.org/manual/tutorial/backup-databases-with-binary-database-dumps/

However, using mongodump and mongorestore to back up and restore MongodDB can be slow. If file system snapshot is an option, you may want to consider using snapshot for MongoDB backup. Information from the following link details two snapshot options for performing hot backup of MongoDB.

http://docs.mongodb.org/manual/tutorial/backup-databases-with-filesystem-snapshots/

You can also look into MongoDB backup service.

http://www.10gen.com/products/mongodb-backup-service