RAID 1+0 is a good choice for a large volume of data.
Distribute the data on many disks. Partition may help.
Use B-Tree in OLTP environment.
Cache the Ref.Tables data in Buffer Pool Keep.
Configure good amount of SORT AREA SIZE.
Configure a large amount for DB_BLOCK_BUFFER.
Check the application Logic.
Avoid Group by, and SORT in SQL statement.
Verify the EXECUTION PLAN for Nested Loops.