How do I know if my Windows Server 2003 has RAID setup?
Is it possible to change the RAID without having to reinstall the OS?You can check the drive management to see if a RAID is setup.

Software RAID is good, but not as good as Hardware RAID where a physical device manages the RAID vs the OS in Software RAID.

Software RAIDs are generally cheaper to set up because you dont need to spend extra money for the Hardware RAID Controller, and generally the Hardware RAID Controller unless an older controller or lower end MFR, will out perform a software RAID which has to rely on system resources while a Hardware RAID is a self contained Resource so it does not usually detract from system performance unless its a lower end controller or old.

Also if the Hardware is a Server, generally the motherboards come with Hardware RAID ready to roll out, tucked into the BIOS.

If you need further assistance, post back and I will point you further in the direction you want to go with your RAID needs to find out more info about it etc.

As far as your question REGARDING if the OS has to be reinstalled, the answer is generally not. Generally you can add drives to build which ever flavor of RAID you want, however I have seen in some occasions with some older controllers where they do not allow for drives to be added after the fact to build a RAID after data is already present. These drives generally will build the RAID, then format and Sync themselves, then will be RAW ready for an OS install.

I would backup your server first just to be sure you have a parachute to fall back on in case you run into a problem. I generally GHOST my systems with Ghost 2003, then test the duplicated drive to make sure it behaves the same as the original drive, then pull the original drive out and set it off to the side as a fail safe, then go forward with adding drives if the system is not a HOT Swapable RAID Controller, or a RAID controller I have never worked with before that I dont know what the OUTCOME would be.

You can also do RESEARCH into the controller, once you figure out the make and model if hardware RAID and see if there are any problems with adding drives or creating a RAID set on a drive with data already present.

Generally Software RAIDs are always forgiving as long as you do not format the drives. You should be able to make a RAID 0 or 1 easily with the OS Software RAID. This will give you the same redundancy and/or spanning that a Hardware RAID will give you, but the performance will be less than a hardware RAID, also Hardware RAIDs are generally better at reporting drive issues vs a Software RAID. Software RAIDs will spill errors into the event log, but if you dont check the event log you will miss that you have lost say one of the drives that make up your mirror and your mirror is broken. The show goes on, but you are flying in dangerous territory since you now have no fault tolerance. This happened to me with my 18 GB software RAID mirror. Fortunately I caught it before the 2nd drive died, so I did not have a total loss!!! Hardware RAIDs generally will have an audio alarm like a Piezo buzzer that will beep loudly when a drive has malfunctioned to alert you to a problem without having to keep and eye in to the event LOGS for trouble.

Hope this helps and is not overwhelming...