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- Backup a Sharded Cluster with Filesystem Snapshots
Backup a Sharded Cluster with Filesystem Snapshots¶
Overview¶
This document describes a procedure for taking a backup of all
components of a sharded cluster. This procedure uses file system
snapshots to capture a copy of the mongod
instance. An
alternate procedure uses mongodump
to create binary
database dumps when file-system snapshots are not available. See
Backup a Sharded Cluster with Database Dumps for the
alternate procedure.
See MongoDB Backup Methods and Backup and Restore Sharded Clusters for a complete information on backups in MongoDB and backups of sharded clusters in particular.
Important
To capture a point-in-time backup from a sharded cluster you must stop all writes to the cluster. On a running production system, you can only capture an approximation of point-in-time snapshot.
Procedure¶
In this procedure, you will stop the cluster balancer and take a backup up of the config database, and then take backups of each shard in the cluster using a file-system snapshot tool. If you need an exact moment-in-time snapshot of the system, you will need to stop all application writes before taking the filesystem snapshots; otherwise the snapshot will only approximate a moment in time.
For approximate point-in-time snapshots, you can improve the quality of the backup while minimizing impact on the cluster by taking the backup from a secondary member of the replica set that provides each shard.
Disable the balancer process that equalizes the distribution of data among the shards. To disable the balancer, use the
sh.stopBalancer()
method in themongo
shell. For example:For more information, see the Disable the Balancer procedure.
Warning
It is essential that you stop the balancer before creating backups. If the balancer remains active, your resulting backups could have duplicate data or miss some data, as chunks may migrate while recording backups.
Lock one secondary member of each replica set in each shard so that your backups reflect the state of your database at the nearest possible approximation of a single moment in time. Lock these
mongod
instances in as short of an interval as possible.To lock a secondary, connect through the
mongo
shell to the secondary member’smongod
instance and issue thedb.fsyncLock()
method.Back up one of the config servers. Backing up a config server backs up the sharded cluster’s metadata. You need back up only one config server, as they all hold the same data
Do one of the following to back up one of the config servers:
Create a file-system snapshot of the config server. Use the procedure in Backup and Restore with Filesystem Snapshots.
Important
This is only available if the config server has journaling enabled. Never use
db.fsyncLock()
on config databases.Use
mongodump
to backup the config server. Issuemongodump
against one of the configmongod
instances.If you are running MongoDB 2.4 or later with the
--configsvr
option, then include the--oplog
option when runningmongodump
to ensure that the dump includes a partial oplog containing operations from the duration of the mongodump operation. For example:
Back up the replica set members of the shards that you locked. You may back up the shards in parallel. For each shard, create a snapshot. Use the procedure in Backup and Restore with Filesystem Snapshots.
Unlock all locked replica set members of each shard using the
db.fsyncUnlock()
method in themongo
shell.Re-enable the balancer with the
sh.setBalancerState()
method.Use the following command sequence when connected to the
mongos
with themongo
shell: