[[backup]]
=== Back Up Your Data!

Always back up your data before performing an upgrade.  This will allow you to
roll back in the event of a problem.  The upgrades sometimes include upgrades
to the Lucene libraries used by Elasticsearch to access the index files, and
after an index file has been updated to work with a new version of Lucene, it
may not be accessible to the versions of Lucene present in earlier
Elasticsearch releases.

[WARNING]
.Always back up your data before upgrading
=========================================
You cannot roll back to an earlier version unless you have a backup of your data.
=========================================

==== Backing up 1.0 and later

To back up a running 1.0 or later system, it is simplest to use the snapshot
feature.  See the complete instructions for
<<modules-snapshots,backup and restore with snapshots>>.

==== Backing up 0.90.x and earlier

To back up a running 0.90.x system:

===== Step 1: Disable index flushing

This will prevent indices from being flushed to disk while the backup is in
process:

[source,json]
-----------------------------------
PUT /_all/_settings
{
  "index": {
    "translog.disable_flush": "true"
  }
}
-----------------------------------
// AUTOSENSE

===== Step 2: Disable reallocation

This will prevent the cluster from moving data files from one node to another
while the backup is in process:

[source,json]
-----------------------------------
PUT /_cluster/settings
{
  "transient": {
    "cluster.routing.allocation.disable_allocation": "true"
  }
}
-----------------------------------
// AUTOSENSE

===== Step 3: Backup your data

After reallocation and index flushing are disabled, initiate a backup of
Elasticsearch's data path using your favorite backup method (tar, storage
array snapshots, backup software).

===== Step 4: Reenable allocation and flushing

When the backup is complete and data no longer needs to be read from the
Elasticsearch data path, allocation and index flushing must be re-enabled:

[source,json]
-----------------------------------
PUT /_all/_settings
{
  "index": {
    "translog.disable_flush": "false"
  }
}

PUT /_cluster/settings
{
  "transient": {
    "cluster.routing.allocation.disable_allocation": "false"
  }
}
-----------------------------------
// AUTOSENSE