Defragmentation and RAID

I saw an article recently about Defragmentation and RAID sets. I am unable to locate that article. So I do not know if it will answer my questions.

1. Should I defragment my RAID set?
2. If so, will the Windows defragmentation tool work on RAID sets? And will it cause problems.
3. If I should defragment but avoid the Windows tool, what are good options?

Thank you,

Rollin Grossholz