In this post, I am sharing required steps to move MySQL Data Directory from old location to new location.

Check the current data directory of MySQL:

mysql> select @@datadir;
+-----------------+
| @@datadir       |
+-----------------+
| /var/lib/mysql/ |
+-----------------+

Stop the MySQL Service:

sudo systemctl stop mysql

Confirm the inactive status of MySQL Service:

sudo systemctl status mysql

● mysql.service - MySQL Community Server
   Loaded: loaded (/lib/systemd/system/mysql.service; enabled; vendor preset: enabled)
   Active: inactive (dead) since Wed 2017-07-12 19:45:48 UTC; 11s ago
 Main PID: 8841 (code=exited, status=0/SUCCESS)

Jul 12 19:11:30 ip-172-31-27-19 systemd[1]: Starting MySQL Community Server...
Jul 12 19:11:31 ip-172-31-27-19 systemd[1]: Started MySQL Community Server.
Jul 12 19:45:46 ip-172-31-27-19 systemd[1]: Stopping MySQL Community Server...
Jul 12 19:45:48 ip-172-31-27-19 systemd[1]: Stopped MySQL Community Server.

Use rsync with -av flag to copy the existing database directory to the new location:

sudo rsync -av /var/lib/mysql /mnt/dbrnd_mysql

Rename old MySQL Data Directory:

sudo mv /var/lib/mysql /var/lib/mysql.backup

Change (datadir=) parameter in MySQL Config file (mysqld.cnf) for pointing to the New Data Location:

sudo nano /etc/mysql/mysql.conf.d/mysqld.cnf

[mysqld]
#
# * Basic Settings
#
user            = mysql
pid-file        = /var/run/mysqld/mysqld.pid
socket          = /var/run/mysqld/mysqld.sock
port            = 3306
basedir         = /usr
datadir         = /mnt/dbrnd_mysql/mysql
tmpdir          = /tmp
lc-messages-dir = /usr/share/mysql
skip-external-locking

Now, Check below sample error:

Job for mysql.service failed because the control process exited with error code. See "systemctl status mysql.service" and "journalctl -xe" for details.

To avoid above error, configure AppArmor Access Control Rules:

AppArmor: AppArmor (“Application”) is a Linux kernel security module that allows the system administrator to restrict programs’ capabilities with per-program profiles. Profiles can allow capabilities like network access, raw socket access, and the permission to read, write, or execute files on matching paths.

Open AppArmor for edit:

sudo nano /etc/apparmor.d/tunables/alias

Add new entry of new data location path:

alias /var/lib/mysql/ -> /mnt/volume-nyc1-01/mysql/,

# ------------------------------------------------------------------
#
#    Copyright (C) 2010 Canonical Ltd.
#
#    This program is free software; you can redistribute it and/or
#    modify it under the terms of version 2 of the GNU General Public
#    License published by the Free Software Foundation.
#
# ------------------------------------------------------------------

# Alias rules can be used to rewrite paths and are done after variable
# resolution. For example, if '/usr' is on removable media:
# alias /usr/ -> /mnt/usr/,
#
# Or if mysql databases are stored in /home:
# alias /var/lib/mysql/ -> /var/lib/mysql/,
alias /var/lib/mysql/ -> /mnt/dbrnd_mysql/mysql/,

After change, restart the AppArmor:

sudo systemctl restart apparmor

Create the minimal directory structure:

sudo mkdir /var/lib/mysql/mysql -p

Now, Start the MySQL Service:

sudo systemctl start mysql

Check the status of MySQL Service:

sudo systemctl status mysql

Now, connect MySQL and check the new datadir location:

mysql> select @@datadir;
+-------------------------+
| @@datadir               |
+-------------------------+
| /mnt/dbrnd_mysql/mysql/ |
+-------------------------+