Generally you would use a raid controller to setup raid, and the OS wouldn't actually be aware of the fact that it had a raid set. There are some OS's that support software Raid, but if you have a machine built within the last 4 or 5 year's it probably has a raid controller on it that you should use.
suppose there exists the software raid then there is no need to hardware raid controller.
Then the raid levels we consider depends on the os support
So i want to know which os's supports which raid levels?