Best way to migrate a 200 GB database from PG 2.7 to 3.6

Dear List,

I need to migrate my database from a 2.x to 3.x. Usually Im using
pg_basebackup , but this is not possible with different versions.
Pg_dump seems to be an option but it is slow like hell and I dont want
to stay offline all the time.
Is there another possibility to migrate  a database with 200 GB ?

Thanks a lot,

cheers

Filip