Hi all, Problem solved, with 2 WD HDDs and "Raid on" mode I`m installing windows server 2008 r2 in UEFI mode, after this system beginning normal boot from raid(mirror). 
Hi, i have problem with installing server 2008 r2 on PowerEdge T20 server I have 2 HDDs WD 1Tb, and make raid 1. when i installing server 2008 r2, i don`t have any problems or errors with this. after installing server, system going to reboot, and give me error "no boot device found" if i choice in bios AHCI mode, everything is ok and server runs. I think problem with "Raid on" mode, and i don`t know how fix it, help me please. 
PowerEdge T20 raid 1 and 2008 r2