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source/tutorial/prepare-for-maintenance.txt

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@@ -11,9 +11,13 @@ Prepare for Cluster Maintenance
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:class: singlecol
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|mms| performs a :opsmgr:`rolling restart </reference/glossary/#std-term-rolling-restart>` when you perform maintenance
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on nodes in a cluster. {+aagent+} updates nodes in a cluster one-by-one
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until all nodes are updated to maintain cluster availability during a
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maintenance period.
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on nodes in a cluster. To maintain cluster availability during a
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maintenance period, {+aagent+} updates nodes in a cluster in the
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following way:
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- For three-member replica sets, {+aagent+} updates nodes one node at a
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time.
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- For five-member replica sets, {+aagent+} updates two nodes at a time.
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Before you perform maintenance on your clusters, review the following
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considerations and take action, if necessary, to maintain cluster
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---------------
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Nodes undergoing maintenance don't provide failover support to the
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cluster. For three-member replica sets, if an additional node becomes
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unavailable while one node is undergoing maintenance, the cluster has
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lost the majority of nodes. The primary node loses this status and
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cluster. For three-member and five-member replica sets, if an
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additional node becomes unavailable during maintenance, the cluster
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loses the majority of nodes. The primary node loses this status and
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steps down to become a secondary node. A new primary can't be elected
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until a majority of the cluster's nodes are available.
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until a majority of the cluster's nodes become available.
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For mission-critical applications with high uptime needs, consider
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converting a three-member replica set to a five-member replica
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set before performing maintenance to maintain cluster majority in case
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:ref:`adding a temporary arbiter <add-member-to-rs>` to a
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three-member or five-member replica set before you perform maintenance.
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The temporary arbiter can maintain cluster majority in case
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an additional cluster node becomes unavailable during a maintenance
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period.
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.. note::
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Five-member replica sets or larger are more resilient and less likely
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to experience loss of majority during maintenance periods.
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A simpler but less resilient option to increase multiple failure
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tolerance is to :ref:`add a temporary arbiter <add-member-to-rs>` to a
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three-member replica set before you perform maintenance.
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Unique Index Builds
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-------------------
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