First, you should be working with your Oracle DBA. If you and the DBA don't work together then you are wasting your time.
Now that I'm off the soap box,...
Check out the following info docs at Sunsolve:
Persistent Write contention How to tune (examples with Oracle)
IPC parameters - ora.init examples
Be aware your version of Oracle isn't supported anymore (except with an extened contract) and you won't be able to use it if you upgrade to Solaris 9 (
Compatibility matrix ).
Another factor may be your choice of DiskSuite over Veritas. Only opinion but I've never seen Oracle without Veritas on Sun - it's just not worth it when dealing with Oracle.
Can you post your /etc/system file? There should be changes made for the Oracle processes.
You should also be looking at the Oracle log files for errors - it may be that there are changes on the Oracle side that really need to be done. Also, what exactly is on the one disk that you are showing as having a problem? How many different databases are there (on that disk and all)? Are the logging files on different drives than the database(s)? Who is running what inside Oracle when you see these problems (sorts inside Oracle will kill a server)?