puoi provare a montare la partizione dove vuoi mettere i database
copiarci /var/lib/mysql

poi correggere my.cnf

datadir = /var/lib/mysql
in datadir = /db

o /mnt/db o dove monti la partizione

http://dev.mysql.com/doc/refman/5.0/...variables.html
---------------
#

datadir
Name datadir
Description Path to the database root
Option Sets Variable Yes, datadir
Variable Name datadir
Variable Scope Global
Dynamic Variable no
Value Set
Type filename

The MySQL data directory. This variable can be set with the --datadir option.
-------------