The process involved in safely disabling data-at-rest encryption for your Aria tables is very similar to that of enabling encryption. To disable, you need to set the relevant system variables and then rebuild each table into an unencrypted state.

Disabling Encryption on User-created Tables

With tables that the user creates, you can disable encryption by setting the aria_encrypt_tables system variable to OFF. Once this is set, MariaDB no longer encrypts new tables created with the Aria storage engine.

SET GLOBAL aria_encrypt_tables = OFF;

Unlike InnoDB, Aria does not currently use background encryption threads. Before removing the Encryption Key Management plugin from the configuration file, you first need to manually rebuild each table to an unencrypted state.

To find the encrypted tables, query the Information Schema, filtering the TABLES table for those that use the Aria storage engine and the PAGE ROW_FORMAT.

SELECT TABLE_SCHEMA, TABLE_NAME
FROM information_schema.TABLES
WHERE ENGINE = 'Aria'
  AND ROW_FORMAT = 'PAGE'
  AND TABLE_SCHEMA != 'information_schema';

Each table in the result-set was potentially written to disk in an encrypted state. Before removing the configuration for the encryption keys, you need to rebuild each of these to an unencrypted state. This can be done with an ALTER TABLE statement.

ALTER TABLE test.aria_table ENGINE = Aria ROW_FORMAT = PAGE;

Once all of the Aria tables are rebuilt, they're safely unencrypted.

Disabling Encryption for Internal On-disk Temporary Tables

MariaDB routinely creates internal temporary tables. When these temporary tables are written to disk and the aria_used_for_temp_tables system variable is set to ON, MariaDB uses the Aria storage engine.

To decrypt these tables, set the encrypt_tmp_disk_tables to OFF. Once set, all internal temporary tables that are created from that point on are written unencrypted to disk.