Gluster users - Dec 2009 - NewBee question: use severals directories on cluster

I'm a Gluster newbee.
Currently i'm trying to build a cyrus-imap cluster.
Cyrus-imap use 2 directories

/var/spool/cyrus
/var/lib/cyrus

When i read examples see in configuration file there is only one posix
folder :

volume posix
  type storage/posix
  option directory /export/gfs
end-volume

My question is : 
is it possible to specify more than one directory  in the configuration
file ? howto ?

best regards