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DOCSP-33391 Sharded Backup with Filesystem Snapshot (#5553) (#5949)
* DOCSP-33391 Fixes filesystem snapshot text * Adds step to find a backup window * Reworks procedure for filesystem snapshot * Refactors filesystem backup * removes deprecated YAML * fixes build error * fixes build error * Fixes per Ian * Fixes per Ashley * Fixes per Ashley * Fixes per Ashley * Fixes build issues * Fixes per Nandini * Fixes per Nandini * Fixes spacing issue * Vale checks --------- Co-authored-by: Ashley Brown <[email protected]>
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‎source/includes/note-shard-cluster-backup.rst‎

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.. important::
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.. important::
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To capture a consistent backup from a sharded
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cluster you **must** stop *all* writes to the cluster.
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To back up a sharded cluster you **must** stop *all* writes to the cluster.

‎source/includes/sharded-clusters-backup-restore-file-system-snapshot-restriction.rst‎

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In MongoDB 4.2+, you cannot use :doc:`file system snapshots
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</tutorial/backup-with-filesystem-snapshots>` for backups that involve
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transactions across shards because those backups do not maintain
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atomicity. Instead, use one of the following to perform the backups:
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To take a backup with a file system snapshot, you must first stop the balancer,
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stop writes, and stop any schema transformation operations on the cluster.
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MongoDB provides backup and restore operations that can run with the balancer
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and running transactions through the following services:
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- `MongoDB Atlas <https://docs.atlas.mongodb.com/>`_
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‎source/tutorial/backup-sharded-cluster-with-filesystem-snapshots.txt‎

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.. default-domain:: mongodb
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.. contents:: On this page
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:local:
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:backlinks: none
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:depth: 1
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:class: singlecol
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Overview
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--------
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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.. include:: /includes/fact-aes256-backups.rst
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Balancer
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~~~~~~~~
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It is *essential* that you stop the :ref:`balancer
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<sharding-internals-balancing>` before capturing a backup.
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If the balancer is active while you capture backups, the backup
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artifacts may be incomplete and/or have duplicate data, as :term:`chunks
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artifacts may be incomplete or have duplicate data, as :term:`chunks
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<chunk>` may migrate while recording backups.
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Precision
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up of the :term:`config database`, and then take backups of each
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shard in the cluster using a file-system snapshot tool. If you need an
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exact moment-in-time snapshot of the system, you will need to stop all
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application writes before taking the file system snapshots; otherwise
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the snapshot will only approximate a moment in time.
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For approximate point-in-time snapshots, you can minimize the impact on
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the cluster by taking the backup from a secondary member of each
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replica set shard.
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writes before taking the file system snapshots; otherwise the snapshot will
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only approximate a moment in time.
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Consistency
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~~~~~~~~~~~
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If the journal and data files are on the same logical volume, you can
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use a single point-in-time snapshot to capture a consistent copy of the
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data files.
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If the journal and data files are on different file systems, you must
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use :method:`db.fsyncLock()` and :method:`db.fsyncUnlock()` to ensure
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that the data files do not change, providing consistency for the
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purposes of creating backups.
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To back up a sharded cluster, you must use the :dbcommand:`fsync` command or
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:method:`db.fsyncLock` method to stop writes on the cluster. This ensures that
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data files do not change during the backup.
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.. include:: /includes/fact-backup-snapshots-with-ebs-in-raid10.rst
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Procedure
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---------
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Steps
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-----
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To take a self-managed backup of a sharded cluster, complete the following
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steps:
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.. procedure::
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:style: normal
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.. step:: Find a Backup Window
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Chunk migrations, resharding, and schema migration operations can cause
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inconsistencies in backups. To find a good time to perform a backup,
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monitor your application and database usage and find a time when these
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operations are unlikely to occur.
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For more information, see :ref:`sharded-schedule-backup`.
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.. step:: Stop the Balancer
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To prevent chunk migrations from disrupting the backup, use
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the :method:`sh.stopBalancer` method to stop the balancer:
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.. code-block:: javascript
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sh.stopBalancer()
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If a balancing round is currently in progress, the operation waits for
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balancing to complete.
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To confirm that the balancer is stopped, use the
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:method:`sh.getBalancerState` method:
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.. io-code-block::
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.. input::
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:language: javascript
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sh.getBalancerState()
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.. output::
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:language: javascript
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false
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The command returns ``false`` when the balancer is stopped.
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.. step:: Lock the Cluster
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Writes to the database can cause backup inconsistencies. Lock your
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sharded cluster to protect the database from writes.
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To lock a sharded cluster, use the :method:`db.fsyncLock` method:
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.. code-block:: javascript
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db.getSiblingDB("admin").fsyncLock()
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Run the following aggregation pipeline on both :program:`mongos` and
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the primary :program:`mongod` of the config servers. To confirm the
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lock, ensure that the ``fysncLocked`` field returns ``true`` and
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``fsyncUnlocked`` field returns ``false``.
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.. io-code-block::
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.. input::
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:language: javascript
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db.getSiblingDB("admin").aggregate( [
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{ $currentOp: { } },
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{ $facet: {
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"locked": [
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{ $match: { $and: [
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{ fsyncLock: { $exists: true } },
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{ fsyncLock: true }
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] } }],
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"unlocked": [
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{ $match: { fsyncLock: { $exists: false } } }
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]
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} },
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{ $project: {
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"fsyncLocked": { $gt: [ { $size: "$locked" }, 0 ] },
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"fsyncUnlocked": { $gt: [ { $size: "$unlocked" }, 0 ] }
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} }
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] )
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.. output::
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:language: json
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[ { fsyncLocked: true }, { fsyncUnlocked: false } ]
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.. step:: Back up the Primary Config Server
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.. note::
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Backing up a :ref:`config server <sharding-config-server>` backs
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up the sharded cluster's metadata. You only need to back up one
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config server, as they all hold the same data. Perform this step
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against the CSRS primary member.
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To create a filesystem snapshot of the config server, follow the
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procedure in :ref:`lvm-backup-operation`.
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.. step:: Back up the Primary Shards
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Perform a filesystem snapshot against the primary member of each shard,
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using the procedure found in :ref:`backup-restore-filesystem-snapshots`.
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.. step:: Unlock the Cluster
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After the backup completes, you can unlock the cluster to allow writes
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to resume.
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To unlock the cluster, use the :method:`db.fsyncUnlock` method:
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.. code-block:: bash
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db.getSibling("admin").fsyncUnlock()
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Run the following aggregation pipeline on both :program:`mongos` and
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the primary :program:`mongod` of the config servers. To confirm the
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unlock, ensure that the ``fysncLocked`` field returns ``false`` and
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``fsyncUnlocked`` field returns ``true``.
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.. io-code-block::
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.. input::
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:language: javascript
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db.getSiblingDB("admin").aggregate( [
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{ $currentOp: { } },
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{ $facet: {
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"locked": [
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{ $match: { $and: [
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{ fsyncLock: { $exists: true } },
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{ fsyncLock: true }
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] } }],
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"unlocked": [
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{ $match: { fsyncLock: { $exists: false } } }
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]
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} },
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{ $project: {
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"fsyncLocked": { $gt: [ { $size: "$locked" }, 0 ] },
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"fsyncUnlocked": { $gt: [ { $size: "$unlocked" }, 0 ] }
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} }
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] )
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.. output::
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:language: json
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[ { fsyncLocked: false }, { fsyncUnlocked: true } ]
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.. step:: Restart the Balancer
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To restart the balancer, use the :method:`sh.startBalancer` method:
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.. code-block:: javascript
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sh.startBalancer()
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To confirm that the balancer is running, use the
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:method:`sh.getBalancerState` method:
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.. io-code-block::
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.. input::
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:language: javascript
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sh.getBalancerState()
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.. output::
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:language: javascript
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true
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.. include:: /includes/steps/backup-sharded-cluster-with-snapshots.rst
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The command returns ``true`` when the balancer is running.

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