improve number access disk on oracle/linux

hello,

  I have an alert event i/o disk 100% buzy on  dm-3, dm-31, dm-33, dm-5 by the agent Oracle.

Disk Device dm-5 is 98.201% busy.

therefore I controled by oswatcher how and which use these file system.

Then I would like improve the performance of disk by increase the cached disk, block size.

on the graph I saw that I have :

             1 – Why several are until 200,000 I/O per sec and others are only until 120,000 per second ?

             2 - How may I improve it by playing with the number block / read of oracle.

             3 - I try to find if there are a solution to improve the number access.