Migrating Your MariaDB Database in CentOS 7: Addressing datadir Woes

• The default location on CentOS 7 is typically /var/lib/mysql.
• In MariaDB, the data directory (datadir) stores crucial database files, including tables, indexes, and logs.

Why Move the Data Directory?

There are several reasons you might want to relocate the data directory:

• Specific Storage Requirements: You might have specific storage requirements (e.g., SSD for performance) that the default location doesn't meet.
• Accommodate Growth: If you anticipate significant database expansion, moving the data directory to a dedicated partition with ample storage can be beneficial.
• Separate Data from System Files: Isolating data from the operating system files can enhance organization and potentially improve performance.

Steps to Move the Data Directory (with Considerations)

1. Verify Current Location:
   • Log in to your CentOS 7 server.
   • Connect to the MariaDB server using the administrative credentials:

     mysql -u root -p
     

     (Enter your root password when prompted)
   • Once connected, run the following query to find the current datadir:

     SELECT @@datadir;
     

2. Stop MariaDB Service: Ensure MariaDB is not running before making changes:

   sudo systemctl stop mariadb
   

3. Create New Directory:
4. Move Data Files (Cautiously):
   • Caution: Improper data handling can lead to data corruption or loss.
   • Use a tool like rsync for a more robust and potentially faster copy operation:

     sudo rsync -avz /var/lib/mysql/* /path/to/new/datadir
     

   • Alternatively, you can use cp -rp (preserve permissions), but rsync might be preferable in some scenarios.
5. Update MariaDB Configuration:
   • Edit the MariaDB configuration file (/etc/my.cnf):

     sudo nano /etc/my.cnf
     

   • Locate the datadir setting and update it to reflect the new location:

     [mysqld]
     datadir = /path/to/new/datadir
     

   • Save the changes (Ctrl+O, Enter) and exit (Ctrl+X).
6. Adjust SELinux Context (if applicable):
7. Start MariaDB Service: Restart MariaDB to apply the changes:

   sudo systemctl start mariadb
   

8. Verify Successful Start: Check if MariaDB has started successfully using the systemctl command:

   sudo systemctl status mariadb
   

Additional Considerations:

• SELinux: If you encounter issues related to SELinux, consult the MariaDB documentation or relevant resources for guidance on handling SELinux contexts.
• Permissions for ibdata1: The ibdata1 file might require additional permissions (chmod 660 /path/to/new/datadir/ibdata1). Refer to your MariaDB documentation for specific recommendations.
• Permissions: Double-check that the new data directory has the correct ownership and permissions (chown mysql:mysql /path/to/new/datadir).

mysql -u root -p  # Connect to MariaDB server (enter password when prompted)

SELECT @@datadir;  # Get current datadir location

Stop MariaDB Service:

sudo systemctl stop mariadb

Create New Directory (Assuming /mnt/data for new location):

sudo mkdir /mnt/data  # Create directory (replace with your desired location)
sudo chown mysql:mysql /mnt/data  # Set ownership

Move Data Files (Using rsync):

sudo rsync -avz /var/lib/mysql/* /mnt/data  # Robust copy with progress info

Update MariaDB Configuration:

sudo nano /etc/my.cnf  # Edit configuration file

# Locate and update datadir setting
[mysqld]
datadir = /mnt/data  # Replace with your new directory path

# Save changes (Ctrl+O, Enter) and exit (Ctrl+X)

Adjust SELinux Context (if applicable):

sudo semanage fcontext -a -t mysqld_db_t /mnt/data  # Set SELinux context
sudo restorecon -R /mnt/data  # Restore context recursively

sudo systemctl start mariadb

Verify Successful Start:

sudo systemctl status mariadb

• Permissions: Double-check after moving the data directory:

sudo chown mysql:mysql /mnt/data  # Ownership
sudo chmod 660 /mnt/data/ibdata1  # Permissions for ibdata1 (check documentation)

This method creates a symbolic link from the default location (/var/lib/mysql) to your new data directory. It's a quicker approach, but consider its limitations:

• Not Ideal for Long-Term: Symbolic links can introduce complexity in management and troubleshooting.
• Potential Issues: If the link breaks (e.g., due to filesystem changes), MariaDB might not start correctly.

Steps:

1. Stop MariaDB service (sudo systemctl stop mariadb).
2. Create the new directory (same steps as in the primary method).
3. Move data files (optional, only if you want to physically move the data):

   sudo mv /var/lib/mysql/* /path/to/new/datadir
   

4. Create the symbolic link:

   sudo ln -s /path/to/new/datadir /var/lib/mysql
   

Logical Volume Management (LVM):

If you want to leverage LVM for flexibility in storage management, you can create a logical volume and mount it at the desired data directory location. This provides finer control over storage allocation.

Steps (assuming basic LVM knowledge):

1. Create a physical volume (PV) using your desired storage device.
2. Create a logical volume group (VG) using the PV.
3. Create a logical volume (LV) with the appropriate size for your data.
4. Format the LV with the desired filesystem.
5. Mount the LV at the new data directory location.
6. Move data files (optional, same steps as in symbolic link method).
7. Update MariaDB configuration (/etc/my.cnf) as in the primary method, replacing the datadir with the mounted LV path.

Important Notes:

• Ensure your LVM setup is stable and reliable to avoid potential data accessibility issues.
• LVM configuration involves additional steps and requires a solid understanding of LVM concepts. Refer to LVM documentation for detailed instructions.

Choosing the Right Method:

• If you require more granular storage management and are comfortable with LVM, consider the LVM approach.
• For a simple relocation with minimal complexity, the primary method (copying and updating configuration) or the symbolic link method (if data movement isn't crucial) might be suitable.