I have a Mac Pro which has 3 internal 1TB Hard Drives. The first drive is the main system drive and the 2nd and 3rd are both used as a 'server drive' which I share and use with all the laptops in my office. This 2nd and 3rd server drive are set up as a RAID slice. Everything has gone well except for until around 3-4 weeks ago whenever I would restart the Mac pro it made a strange sound. I don't know how to describe it but at first I thought it was one of the fans on the graphics cards or the fan on the power supply but I ruled that out. It seems that it's coming from one of the hard drives. It only makes the sound at bootup and then it's fine. I looked at Disc Utility and saw the following: The 1TB drive that's used as the RAID is listed at the top which it saying just below: RAID Slice for 'Server Drive' Then it lists my Macintosh HD and below that it lists: 999.86 GB Server Drive and below that says Server Drive When I click on 999.86 GB Server Drive it says for RAID Status: Degraded The type of RAID I'm using is the Mirrored RAID Set If I click on the RAID tab while selecting the RAID drive I get the following: 999.86 GB 'Server Drive' Mirrored RAID Set: Degraded 999.86 GB Raid Slice (disk0s2) RAID Slice (and some long number): Missing I don't know what's going on here. Because of the noise I'm assuming one of the drives is either in the processing of failing or has already failed. From looking at the above information I get the same feeling. I have a program called Data Rescue 3 which I have run on all 3 drives and it's showing them as healthy. Does anyone know what the above means? Is there a hardware problem with my drive or is there an issue with a setting on the RAID that can be corrected through OS X? Thank you for your help.