The ultimate limit on I/O performance is dictated by the number of devices available, and the spread of data across these devices. You should ensure that there are a sufficient number of disks to support your projected I/O rates. You should also ensure that data is spread as evenly as possible across these disks, and that there are no disk hot-spots.
There are three ways to spread data across devices. They are:
RAID 5 can decrease write performance unless the raid array is associated with a battery-backed memory cache (and quite often even then).
Generally, RAID 0 is recommended on performance grounds. If RAID 0 is not available, you should manually stripe your tablespaces across multiple devices. Manual (or Oracle) striping is achieved by allocating many small files to each tablespace, and spreading these files across the multiple disks.
Because a table extent must be located within a single database file, tables consisting of a single extent cannot be manually striped. In this case, you must ensure that heavily utilized tables (and indexes) are composed of a large number of extents. You may decide to reduce the size of your data files to that of a single extent (plus a one block overhead).