MongoDB - Unable to change mongodb storage engine to WiredTiger
Based on the warning message included in your description, you are already using the WiredTiger storage engine but your dbPath is using the ext file system (in theory ext4, but the Linux filesystem magic number doesn't distinguish ext2/ext3/ext4). Note: WiredTiger is the default storage engine for MongoDB 3.2+, so there is no need to specify it in your configuration file.

This warning was added for the MongoDB 3.4 production release per SERVER-22606: Startup warning if ext4 is used with WiredTiger. There are some known performance issues with ext4 (in particular, periodic stalls) so this warning is meant to proactively ensure administrators are alerted to potentially problematic configurations. Filesystem and other production caveats are also included in the Production Notes in the MongoDB manual.

To suppress this warning you could either:


Host your dbPath on a supported filesystem other than ext4 (XFS is recommended)
Start your mongo shell with the --quiet parameter (which might suppress other interesting startup info / warnings)


You can certainly choose to ignore startup warningd (particularly for a development environment), but should consider using XFS with WiredTiger if this is a production environment.

You may want to watch/upvote SERVER-19790: Provide mechanism to clear/acknowledge startup warnings, which could allow startup warnings to be ack'd so they do not appear on every new mongo session.