[[snapshot-restore]]
= Snapshot and restore

[partintro]
--

// tag::snapshot-intro[]
A _snapshot_ is a backup taken from a running {es} cluster.
You can take snapshots of an entire cluster, including all its data streams and
indices. You can also take snapshots of only specific data streams or indices in
the cluster.

You must
<<snapshots-register-repository, register a snapshot repository>>
before you can <<snapshots-take-snapshot, create snapshots>>.

Snapshots can be stored in either local or remote repositories.
Remote repositories can reside on Amazon S3, HDFS, Microsoft Azure,
Google Cloud Storage,
and other platforms supported by a {plugins}/repository.html[repository plugin].

Snapshots are incremental: each snapshot only stores data that
is not part of an earlier snapshot.
This enables you to take frequent snapshots with minimal overhead.
// end::snapshot-intro[]

// tag::restore-intro[]
You can <<snapshots-restore-snapshot,restore snapshots>> to a running cluster, which includes all data streams and indices in the snapshot
by default.
However, you can choose to restore only the cluster state or specific data
streams or indices from a snapshot.
// end::restore-intro[]

You can use
<<getting-started-snapshot-lifecycle-management, {slm}>>
to automatically take and manage snapshots.

// tag::backup-warning[]
WARNING: You cannot back up an {es} cluster by simply copying
the data directories of all of its nodes. {es} 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::backup-warning[]

[discrete]
[[snapshot-restore-version-compatibility]]
=== Version compatibility

IMPORTANT: Version compatibility refers to the underlying Lucene index
compatibility. Follow the <<setup-upgrade,Upgrade documentation>>
when migrating between versions.

A snapshot contains a copy of the on-disk data structures that make up an
index or a data stream's backing indices. This means that snapshots can only be restored to versions of
{es} that can read the indices:

* A snapshot of an index created in 6.x can be restored to 7.x.
* A snapshot of an index created in 5.x can be restored to 6.x.
* A snapshot of an index created in 2.x can be restored to 5.x.
* A snapshot of an index created in 1.x can be restored to 2.x.

Conversely, snapshots of indices created in 1.x **cannot** be restored to 5.x
or 6.x, snapshots of indices created in 2.x **cannot** be restored to 6.x
or 7.x, and snapshots of indices created in 5.x **cannot** be restored to 7.x
or 8.x.

We do not recommend restoring snapshots from later {es} versions in earlier
versions. In some cases, the snapshots cannot be restored. For example, a
snapshot taken in 7.6.0 cannot be restored to 7.5.0.

Each snapshot can contain indices created in various versions of {es}. This
includes backing indices created for data streams. When restoring a snapshot, it
must be possible to restore all of these indices into the target cluster. If any
indices in a snapshot were created in an incompatible version, you will not be
able restore the snapshot.

IMPORTANT: When backing up your data prior to an upgrade, keep in mind that you
won't be able to restore snapshots after you upgrade if they contain indices
created in a version that's incompatible with the upgrade version.

If you end up in a situation where you need to restore a snapshot of a data stream or index
that is incompatible with the version of the cluster you are currently running,
you can restore it on the latest compatible version and use
<<reindex-from-remote,reindex-from-remote>> to rebuild the data stream or index on the current
version. Reindexing from remote is only possible if the original data stream or index has
source enabled. Retrieving and reindexing the data can take significantly
longer than simply restoring a snapshot. If you have a large amount of data, we
recommend testing the reindex from remote process with a subset of your data to
understand the time requirements before proceeding.

--

include::register-repository.asciidoc[]
include::take-snapshot.asciidoc[]
include::restore-snapshot.asciidoc[]
include::monitor-snapshot-restore.asciidoc[]
include::delete-snapshot.asciidoc[]
include::../slm/index.asciidoc[]
