• Ops Manager Backup Software (page 186) 

## Backup by Copying Underlying Data Files 

You can create a backup by copying MongoDB’s underlying data files. 

If the volume where MongoDB stores data files supports point in time snapshots, you can use these snapshots to create backups of a MongoDB system at an exact moment in time. 

File systems snapshots are an operating system volume manager feature, and are not specific to MongoDB. The mechanics of snapshots depend on the underlying storage system. For example, if you use Amazon’s EBS storage system for EC2 supports snapshots. On Linux the LVM manager can create a snapshot. 

To get a correct snapshot of a running mongod process, you must have journaling enabled and the journal must reside on the same logical volume as the other MongoDB data files. Without journaling enabled, there is no guarantee that the snapshot will be consistent or valid. 

To get a consistent snapshot of a sharded system, you must disable the balancer and capture a snapshot from every shard and a config server at approximately the same moment in time. 

If your storage system does not support snapshots, you can copy the files directly using cp , rsync , or a similar tool. Since copying multiple files is not an atomic operation, you must stop all writes to the mongod before copying the files. Otherwise, you will copy the files in an invalid state. 

Backups produced by copying the underlying data do not support point in time recovery for replica sets and are difficult to manage for larger sharded clusters. Additionally, these backups are larger because they include the indexes and duplicate underlying storage padding and fragmentation. mongodump , by contrast, creates smaller backups. 

For more information, see the Backup and Restore with Filesystem Snapshots (page 243) and Backup a Sharded Cluster with Filesystem Snapshots (page 256) for complete instructions on using LVM to create snapshots. Also see Back up and Restore Processes for MongoDB on Amazon EC2$^{1}$. 

## Backup with mongodump 

The mongodump tool reads data from a MongoDB database and creates high fidelity BSON files. The mongorestore tool can populate a MongoDB database with the data from these BSON files. These tools are simple and efficient for backing up small MongoDB deployments, but are not ideal for capturing backups of larger systems. 

mongodump and mongorestore can operate against a running mongod process, and can manipulate the underly- ing data files directly. By default, mongodump does not capture the contents of the local database (page 652). 

mongodump only captures the documents in the database. The resulting backup is space efficient, but mongorestore or mongod must rebuild the indexes after restoring data. 

When connected to a MongoDB instance, mongodump can adversely affect mongod performance. If your data is larger than system memory, the queries will push the working set out of memory. 

To mitigate the impact of mongodump on the performance of the replica set, use mongodump to capture back- ups from a secondary (page 567) member of a replica set. Alternatively, you can shut down a secondary and use mongodump with the data files directly. If you shut down a secondary to capture data with mongodump ensure that the operation can complete before its oplog becomes too stale to continue replicating. 

For replica sets, mongodump also supports a point in time feature with the --oplog option. Applications may continue modifying data while mongodump captures the output. To restore a point in time backup created with --oplog , use mongorestore with the --oplogReplay option. 

