Backup MySQL databases to external hard drive then restore
Use mysqldump from the command line.

For example, to dump all your databases to a file, use the --all-databases switch and a result file for output:

mysqldump [options] --all-databases --result-file=dump.sql


If the DBs are big, you can split them out into their own files. The dump command is flexible like that.

(Ref: https://dev.mysql.com/doc/refman/5.7/en/mysqldump.html)

To restore, all you have to do is run the dump file as a script, which you can also do from the command line.