I want to create a RAID 5 array in windows 8 with 5 Dynamic Hard Disks and it is grayed out.

If this is not possible why not hide that option.  

If it is possible why it is disabled? 

after your questions i share this article for you ...
["New RAID-5 Volume..." greyed out in Disk Management](http://social.technet.microsoft.com/Forums/en/w7itproinstall/thread/a1851e42-c705-4558-920c-30ba7c6cf080)