By user702295-Oracle on Mar 06, 2012
Recommendation for Demantra?
If you are using a striped storage device, be it striped in hardware (like RAID 1+0 or RAID 5) or striped in software over many disks, then there is less of a need to separate the DB objects into different tablespaces as OATM constructs.
When doing an index lookup the DB server reads from the index and then it reads from the data table. If both the index and the table are on the same physical disk then the DB server will wait between the index read and the data read while the disk head moves and the disk spins around to the right spot.
But if your storage device is an array of many disks then odds are that the index block and the data table block are not on the same physical disk anyway. The more disks in the array the lower the odds that the DB server will need to wait.
That is why the number of disks is more important than their size. The more disks the faster the I/O.