hm then how come in Compaq servers I do see /dev/dsk/c0t0d0s0 but not in Dell servers

I am having a problem is in a Compaq Server everything is fast and smooth but in a Dell server database is extremely slow, whenever there is some batch job or a big update going I start to see free buffer waits in v$session_wait and noone can get in. I have patched to 8.1.7.4 since there was a bug which cause buffer waits in 8.1.7.0.1 but after patching I still have the same problem so I suspect it's a OS configuration problem. I am trying to find out how to determine if async i/o is used in Linux. The other difference I noticed is that Compaq sees the SCSI Adapter perfectly but not in Dell althoguh I am not 100% sure if this is the problem.
Basically I am trying to determine what is the difference between the Compaq Server and Dell server at OS level (not the hardware since the SGA settings are similar). I am ignoring RAID now even Dell is running on RAID 5 and Compaq on RAID 0+1 because although RAID 5 is slow I dont believe a simple update of 500000 rows would lock the whole database with free buffer waits

I have increased db writer with no luck