I have installed with the help of following link: https://www.digitalocean.com/community/tutorials/how-to-install-mongodb-on-ubuntu-16-04

It was working fine by default. But when I change data directory in /etc/mongod.conf

#From
dbPath: /var/lib/mongodb
#To
dbPath: /media/user/'Mounted Volume'/mongodb_data

I am unable to start MongoDB. Following is the error message

$mongo
MongoDB shell version: 3.2.11
connecting to: test
2017-01-06T00:57:01.472+0530 W NETWORK  [thread1] Failed to connect to 127.0.0.1:27017, reason: errno:111 Connection refused
2017-01-06T00:57:01.472+0530 E QUERY    [thread1] Error: couldn't connect to server 127.0.0.1:27017, connection attempt failed :
connect@src/mongo/shell/mongo.js:229:14
@(connect):1:6

exception: connect failed

Following is the status

$ sudo systemctl status mongodb
 mongodb.service - High-performance, schema-free document-oriented database
Loaded: loaded (/etc/systemd/system/mongodb.service; enabled; vendor preset: 
Active: failed (Result: exit-code) since Fri 2017-01-06 00:56:40 IST; 7s ago
Process: 5735 ExecStart=/usr/bin/mongod --quiet --config /etc/mongod.conf (cod
Main PID: 5735 (code=exited, status=100)

Jan 06 00:56:40 GL552VW systemd[1]: Started High-performance, schema-free docume
Jan 06 00:56:40 GL552VW systemd[1]: mongodb.service: Main process exited, code=e
Jan 06 00:56:40 GL552VW systemd[1]: mongodb.service: Unit entered failed state.
Jan 06 00:56:40 GL552VW systemd[1]: mongodb.service: Failed with result 'exit-co

I am new to MongoDB. Maybe I am missing something very simple.