How to disable SCSI write cache on RHEL

Hi,
 
Does anyone know how to disable filesystem cache at Linux (RHEL4) level?  I 
know it can be disable using filesytemio_options=directio|setall init.ora 
parameters. But that does not protect the other non-database files in case of 
server crash. We already have SAN attached disks, so there is plenty of SAN 
cache to speed up the things. I want to avoid the risk of filesytem corruption 
on linux server crash due to filesystem buffering/caching. 
 
Someone on internet mentioned, one of the way is by executing following 
command, but which is the config file which needs to be updated to make things 
more persistent.
 
echo 1 > /proc/scsi/sg/allow_dio
 
Regards,
Vishal Gupta

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