innodb_buffer_pool & innodb_buffer_pool_instances
The number of pools does not change the total amount of pages innodb would use. A page exists on one of the pools, not a copy of it in each pool. That's why your 6GB database doesn't take much more than 6GB, the extra probably being for indexes.

From the documentation:

http://dev.mysql.com/doc/refman/5.6/en/innodb-parameters.html#sysvar_innodb_buffer_pool_instances


  The number of regions that the InnoDB buffer pool is divided into. For
  systems with buffer pools in the multi-gigabyte range, dividing the
  buffer pool into separate instances can improve concurrency, by
  reducing contention as different threads read and write to cached
  pages. Each page that is stored in or read from the buffer pool is
  assigned to one of the buffer pool instances randomly, using a hashing
  function. Each buffer pool manages its own free lists, flush lists,
  LRUs, and all other data structures connected to a buffer pool, and is
  protected by its own buffer pool mutex.