[DOCS] Adds administering section (#43493)

docs/reference/administering.asciidoc

@@ -0,0 +1,25 @@
+[[administer-elasticsearch]]
+= Administering {es}
+
+[partintro]
+--
+Elasticsearch is a complex piece of software, with many moving parts. There are
+many APIs and features that are designed to help you manage your Elasticsearch
+cluster.
+
+--
+
+[[backup-cluster]]
+== Back up a cluster
+
+As with any software that stores data, it is important to routinely back up your
+data. {es} replicas provide high availability during runtime; they enable you to
+tolerate sporadic node loss without an interruption of service.
+
+Replicas do not provide protection from catastrophic failure, however. For that,
+you need a real backup of your cluster—a complete copy in case something goes
+wrong.
+
+To back up your cluster, you can use the <<modules-snapshots,snapshot API>>.
+
+include::{es-repo-dir}/modules/snapshots.asciidoc[tag=snapshot-intro]

docs/reference/index.asciidoc

@@ -67,6 +67,8 @@ include::rollup/index.asciidoc[]
 
 include::frozen-indices.asciidoc[]
 
+include::administering.asciidoc[]
+
 include::rest-api/index.asciidoc[]
 
 include::commands/index.asciidoc[]

docs/reference/modules/snapshots.asciidoc

@@ -1,29 +1,32 @@
 [[modules-snapshots]]
 == Snapshot And Restore
 
+// tag::snapshot-intro[]
 A snapshot is a backup taken from a running Elasticsearch cluster. You can take
 a snapshot of individual indices or of the entire cluster and store it in a
 repository on a shared filesystem, and there are plugins that support remote
 repositories on S3, HDFS, Azure, Google Cloud Storage and more.
 
-Snapshots are taken incrementally. This means that when creating a snapshot of
-an index Elasticsearch will avoid copying any data that is already stored in
-the repository as part of an earlier snapshot of the same index. Therefore it
-can be efficient to take snapshots of your cluster quite frequently.
+Snapshots are taken incrementally. This means that when it creates a snapshot of
+an index, Elasticsearch avoids copying any data that is already stored in the
+repository as part of an earlier snapshot of the same index. Therefore it can be
+efficient to take snapshots of your cluster quite frequently.
 
-Snapshots can be restored into a running cluster via the restore API. When
-restoring an index it is possible to alter the name of the restored index as
-well as some of its settings, allowing a great deal of flexibility in how the
-snapshot and restore functionality can be used.
+You can restore snapshots into a running cluster via the
+<<restore-snapshot,restore API>>. When you restore an index, you can alter the
+name of the restored index as well as some of its settings. There is a great
+deal of flexibility in how the snapshot and restore functionality can be used.
 
-WARNING: It is not possible to back up an Elasticsearch cluster simply by
-taking a copy of the data directories of all of its nodes. Elasticsearch may be
-making changes to the contents of its data directories while it is running, and
-this means that copying its data directories cannot be expected to capture a
-consistent picture of their contents. Attempts to restore a cluster from such a
-backup may fail, reporting corruption and/or missing files, or may appear to
-have succeeded having silently lost some of its data. The only reliable way to
-back up a cluster is by using the snapshot and restore functionality.
+WARNING: You cannot back up an Elasticsearch cluster by simply taking a copy of
+the data directories of all of its nodes. Elasticsearch may be making changes to
+the contents of its data directories while it is running; copying its data
+directories cannot be expected to capture a consistent picture of their contents.
+If you try to restore a cluster from such a backup, it may fail and report
+corruption and/or missing files. Alternatively, it may appear to have succeeded
+though it silently lost some of its data. The only reliable way to back up a
+cluster is by using the snapshot and restore functionality.
+
+// end::snapshot-intro[]
 
 [float]
 === Version compatibility
@@ -509,6 +512,7 @@ When a repository is unregistered, Elasticsearch only removes the reference to t
 the snapshots. The snapshots themselves are left untouched and in place.
 
 [float]
+[[restore-snapshot]]
 === Restore
 
 A snapshot can be restored using the following command: