Mongodb replica set with different storage engine

Vijay Mohan

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Oct 8, 2015, 1:37:36 PM10/8/15

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I am working on migrating mongodb 2.6 to 3.0.6, right now both members have latest version, but secondary have wiredTiger storage engine and primary have the default one, now I want to switch the secondary to Primary.

If anyone did this before please let me know if we do that there will be any issue in replication? I need to do this switch to make the other server also in wiredTiger storage engine.

Rhys Campbell

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Oct 8, 2015, 2:19:05 PM10/8/15

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We did this migration recently. No problems with replication regarding this, the manual even mentions it...

As such, you can update members to use the WiredTiger storage engine in a rolling manner. Before changing all the members to use WiredTiger, you may prefer to run with mixed storage engines for some period.

http://docs.mongodb.org/manual/release-notes/3.0-upgrade/

Stephen Steneker

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Oct 11, 2015, 11:30:34 PM10/11/15

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Hi Vijay,

There is an important note on that page if you are mixing 2.6 + 3.0 in your replica set:

Before enabling the new WiredTiger storage engine, ensure that all replica set/sharded cluster members are running at least MongoDB version 2.6.8, and preferably version 3.0.0 or newer.

You should also be wary of running into potential issues with mixed authentication schemes if you haven't upgraded all replica set members to 3.0 yet:

http://docs.mongodb.org/manual/release-notes/3.0-scram/

If all the replica set members are on the same version, you can run different storage engines in the same replica set. As noted, this is usually done as a part of a rolling upgrade to a new storage engine configuration but can also be useful if you want to have members dedicated for different use cases (for example, a hidden secondary with different compression for archival storage).