How to split dumpfiles into multiple files and multiple directories. /* step By Step */

When you Export full database and your database size is big
( like 20gb – 30gb ).
So, How to break dumpfile in two or more pieces.
And
Your Export backup are store in these Hard disk (directory) and these HDD has less space (5gb) and your backup size is (10gb).
That time we can export these backup in 2 HDD (directories). First backup piece is store in default directory and next backup piece is store in another HDD (directory).