Distributing directory over multiple discs ?

[Frank Staals]

Since one of my discs is filling up rather quickly (Say disc A ) while 
an other one stays quite empty (say disc B ) I would like to distribute 
the content of a directory on disc A over both A and B. I know I can 
simply move some of the files over to a sperate directory on disc B but 
is is possible to somehow merge the 2 ? So for example if I would do an 
ls in discA/dir I would also see the files that are stored on 
discB/an/other/dir ? And off-course if this is possible how can I 
acchieve something like that

Regards,

-- 
-Frank Staals