- Administration >
- Administration Tutorials >
- Backup and Recovery >
- Backup and Restore Sharded Clusters >
- Backup a Sharded Cluster with Filesystem Snapshots
Backup a Sharded Cluster with Filesystem Snapshots¶
On this page
Overview¶
Important
The following procedure applies to the MMAPv1 storage engine only.
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 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.
Considerations¶
Balancing¶
It is essential that you stop the balancer before capturing a backup.
If the balancer is active while you capture backups, the backup artifacts may be incomplete and/or have duplicate data, as chunks may migrate while recording backups.
Precision¶
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.
Consistency¶
If the journal and data files are on the same logical volume, you can use a single point-in-time snapshot to capture a valid copy of the data.
If the journal and data files are on different file systems, you must
use db.fsyncLock()
and db.fsyncUnLock()
to capture
a valid copy of your data.
Procedure¶
Important
The following procedure, which includes db.fsyncLock()
and
db.fsyncUnlock()
operations, applies only to MongoDB instances
using MMAPv1 storage engine.
Disable the balancer.¶
Disable the balancer process that equalizes the distribution
of data among the shards. To disable the balancer, use
the sh.stopBalancer()
method in the mongo
shell.
Consider the following example:
For more information, see the Disable the Balancer procedure.
If necessary, lock one secondary member of each replica set in each shard.¶
If your mongod
does not have journaling enabled or your
journal and data files are on different volumes, you must lock
your mongod
before capturing a back up.
If your mongod
has journaling enabled and your journal
and data files are on the same volume, you may skip this step.
If you need to lock the mongod
, attempt to 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.
To lock a secondary, connect through the mongo
shell to the
secondary member’s mongod
instance and issue the
db.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.¶
Do this only if the config server has journaling enabled. Use the procedure in
Backup and Restore with Filesystem Snapshots. Never use
db.fsyncLock()
on config databases.
Create a database dump to backup the config server.¶
Issue mongodump
against one of the config
mongod
instances. If you are
running MongoDB 2.4 or later with the
--configsvr
option, then include the
--oplog
option 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 locked replica set members.¶
If you locked any mongod
instances to capture the backup,
unlock them now.
Unlock all locked replica set members of each shard using the
db.fsyncUnlock()
method in the mongo
shell.
Enable the balancer.¶
Re-enable the balancer with the sh.setBalancerState()
method. Use the following command sequence when connected to the
mongos
with the mongo
shell: