I have 3 WD Raptors in a Raid 5 (Non-5EE) and one drive errored, rebuilt itself on my command, then failed some unknown time later. Within a week or so. I dont reboot this system very often as it doubles as my file server. SO! Got a replacement raptor from WD and put it in. Didnt do anything until I rebooted it. When I did, it asked me in bios (prior to win startup) if I wanted to rebuild it, I said yes and it started up. I opened my Intel Matrix storage controller and viewed the rebuild. It slowly chugged along and when it hit 10%I left it alone and tended to other work. Later in the day when I checked the system, the disk was not rebuilt, and instead showed itself as missing. It was not listed in my array. NOTE: Before I rebooted the system, the missing hard drive icon popped up in my array list, below the 3 hard drives. So I had 3 discs shown, the third with the error on it, and then a missing item below. Now my 3rd disc is gone and the "missing" icon took its place. What happened to the RAID 5 rebuild? I read somewhere that the rebuild is tricky and is not always successful. I wont be able to reboot the system until the end of the day.