I know this has been asked loads before, but...

I have a raspberry pi 3 with an external USB disk mounted at /mnt/database. I can load and run the default install for MariaDB, but when I try to set the datadir = /mnt/database/mysql I get the 'no such file or directory; error. I have tried everything I can find with Google. And I have been trying every day since the start of November for at least two hours a day. Can anyone take me through a foolproof way to do it?

Yours desperately Simon M.