When running MariaDB on your QNAP, you may find tons of files name "mysql-bin.xxxxxx" files (where xxxxxx is a number) in your data dir (for example: /share/CACHEDEV1_DATA/.mariadb10/data).
You should never just randomly delete those, as these are binary logs generated by mysqld - and there are proper SQL statements to clean these up.
PURGE BINARY LOGS TO 'mysql-bin.xxxxxx';
PURGE BINARY LOGS BEFORE 'datetimestamp';
These statement will clear all bin-log files up to the given number (mysql-bin.xxxxxx) or up to a given date (datetimestamp).
For example, the following statement will remove all files numbered prior to "mysql-bin.000123"
PURGE BINARY LOGS TO 'mysql-bin.000123';
You can also use something like this, to remove all bin-log files older than 5 days:
PURGE BINARY LOGS BEFORE DATE(NOW() - INTERVAL 5 DAY) + INTERVAL 0 SECOND;
You can have MySQL/MariaDB clear these bin-log files automatically by sayin, for example, that it should only keep the bin-log files of the last 5 days:
SET GLOBAL expire_logs_days = 5;
You may want to add this to the settings file though (/etc/my.cnf - this will be different on your QNAP, maybe /share/CACHEDEV1_DATA/.qpkg/MariaDB10/etc/mariadb.conf)