vkeven is correct.

To control this you need so called SAN File System programs. SAN file system solutions are very expensive.

Examples are listed below:
MelioFS:
http://www.sanbolic.com/melio.htm
IBM:
http://www-306.ibm.com/software/tivo...ducts/sanergy/
http://www.ibm.qassociates.co.uk/sto...rage-san-files
yste
m.htm
StorNext:
http://www.adic.com/ibeCCtpItmDspRte...24&item=121889
SGI:
http://www.sgi.com/products/storage/...e_systems.html
PolyServe
http://www.polyserve.com/
DataPlow SFS
http://www.dataplow.com