So, where can be stored the MySQL data
directory?
I mean the type of destination location: is outside BASEDIR ok? should be same partition? same disk? maybe a temporary RAM partition is also fine? NFS partition? symlinked to one of these? etc.
Anywhere that the mysql
user can access it is fine. It's just a directory with files, that are read and written normally - there is nothing special about them. It can be a different partition, or even a different disk (e.g. SSD is a good idea). NFS will work, but make sure it's quick (for obvious reasons, really). Symlinks are also perfectly acceptable.
I have run MySQL from a ramdisk before, and it worked perfectly.