MongoDB Documentation, Release 3.0.4 Additional Resources • Blog Post: Improved Password-Based Authentication in MongoDB 3.0: SCRAM Explained (Part 2) 280 • Blog Post: Improved Password-Based Authentication in MongoDB 3.0: SCRAM Explained (Part 1) 279 Downgrade MongoDB from 3.0 Before you attempt any downgrade, familiarize yourself with the content of this document, particularly the Downgrade Recommendations and Checklist (page 821) and the procedure for downgrading sharded clusters (page 823). Downgrade Recommendations and Checklist When downgrading, consider the following: Downgrade Path Once upgraded to MongoDB 3.0, you cannot downgrade to a version lower than 2.6.5 . Important: If you upgrade to MongoDB 3.0 and have run authSchemaUpgrade , you cannot downgrade to the 2.6 series without disabling --auth . Procedures Follow the downgrade procedures: Note: Optional . Consider compacting collections after downgrading. Otherwise, older versions will not be able to reuse free space regions larger than 2MB created while running 3.0. This can result in wasted space but no data loss following the downgrade. Downgrade a Standalone mongod Instance If you have changed the storage engine to WiredTiger , change the storage engine to MMAPv1 before downgrading to 2.6. Change Storage Engine to MMAPv1 To change storage engine to MMAPv1 for a standalone mongod instance, you will need to manually export and upload the data using mongodump and mongorestore . mongodump --out <exportDataDestination> Specify additional options as appropriate, such as username and password if running with authorization enabled. See mongodump for available options. Step 3: Create data directory for MMAPv1. Create a new data directory for MMAPv1. Ensure that the user account running mongod has read and write permissions for the new directory. Step 2: Export the data using mongodump . Step 1: Ensure 3.0 mongod is running with WiredTiger. Downgrade MongoDB Processes • To downgrade sharded clusters, see Downgrade a 3.0 Sharded Cluster (page 823). • To downgrade replica sets, see Downgrade a 3.0 Replica Set (page 822). • To downgrade a standalone MongoDB instance, see Downgrade a Standalone mongod Instance (page 821). $^{279}$https://www.mongodb.com/blog/post/improved-password-based-authentication-mongodb-30-scram-explained-part-1?jmp=docs $^{280}$https://www.mongodb.com/blog/post/improved-password-based-authentication-mongodb-30-scram-explained-part-2?jmp=docs 821 12.1. Current Stable Release