kindly guide me to find which particular process is using more I/O in a disk 
So, what vendor and version of Unix?
What have you tried so far?
There's not much to go on at the moment.
Robin
Describe your environment (system, OS, versions, tuning parameters, ...), then show relevant data (like iostat output, etc.).
So far, I'd say use truss.
I hope this helps.
bakunin