change-replica-set-wiredtiger.txt

================================
Change Replica Set to WiredTiger
================================

.. default-domain:: mongodb

Starting in version 3.2, WiredTiger is the default storage engine
for MongoDB.

This tutorial gives an overview of changing the storage engine of a
:term:`replica set` member to :ref:`WiredTiger
<storage-wiredtiger>`.

Considerations
--------------

Replica sets can have members with different storage engines. As such,
you can update members to use the WiredTiger storage engine in a rolling
fashion.

.. include:: /includes/fact-wiredtiger-minimum-version.rst

Procedure
---------

To update a member to WiredTiger, the procedure removes a member's
data, starts :binary:`~bin.mongod` with WiredTiger, and performs an
:doc:`initial sync </tutorial/resync-replica-set-member>`.

.. tip::

   To update all members of the replica set to use WiredTiger, update
   the members in a rolling manner. That is, update, one by one, all
   :term:`secondary` members first. Then, once all the secondary
   members have been updated, :method:`step down <rs.stepDown()>` the
   :term:`primary`, and update that stepped-down member.

Update a secondary member.
~~~~~~~~~~~~~~~~~~~~~~~~~~

.. container:: admonition

   .. include:: /includes/steps/change-replica-set-wiredtiger.rst

To update another secondary, repeat the previous steps.

Update the primary.
~~~~~~~~~~~~~~~~~~~

.. important::

   If updating all members of the replica set to use WiredTiger, ensure
   that all secondary members have been updated first before updating
   the primary.

To update the primary, :method:`step down <rs.stepDown()>` the
:term:`primary`.

.. container:: admonition

   .. code-block:: javascript

      rs.stepDown()

When the primary has stepped down and become a secondary, update the
secondary to use WiredTiger as before:

.. container:: admonition

   .. include:: /includes/steps/change-replica-set-wiredtiger.rst