Use Oracle Orion Calibration Tool:
Oracle Orion is expressly designed for simulating Oracle database I/O workloads using the same I/O software stack as Oracle. Orion can also simulate the effect of striping performed by Oracle Automatic Storage Management.
Caution: write tests obliterate (DESTROY) all data on the specified LUNS. (so If you will run write test create a small Lun on same storage h/w and perfom test on that LUN)
Or use I/O Calibration Inside the Database
By using DBMS_RESOURCE_MANAGER.CALIBRATE_IO