Now and then I experience something quite alarming and odd when I power up my Mac Pro (model 5,1, 2010, 2.8GHz quad core running OSX 10.6.8): my main hard drive is missing! In other words the Finder disk icon is gone and I get all sorts of "not found" error messages (which I believe are totally legit as this is my "user" drive where I keep all my settings and files). But if I restart the computer the drive mysteriously reappears and everything works as before! My Mac Pro is set up with multiple internal hard drives: System (an SSD with OSX, all my apps, administrator user area) Time Machine (regular Time Machine backups) User (my main user area with all my files, settings etc.) Emergency backup (a bootable clone of all my drives (using Chronosync) which is automatically done every 2-3 hours) Cache (SSD used for Lightroom, Photoshop, Adobe Bridge etc. cache and temporary files) It's the "User" drive that has had the problems mentioned above, and it happened again today. I decided to try running Disk Utility when the drive had disappeared but couldn't get it to launch. Most likely because I use Alfred for keyboard shortcuts, and my settings were on that drive. I should have launched it directly from the /Applications/ folder on my system drive instead, silly me, to see if the drive was unmounted or simply not there. I'll see about that next time. S.M.A.R.T. status is OK, but then again I have had past experiences with drives that show "OK" but in reality are starting to fail (resulting in several corrupt files). Could the drive be failing? What do you suggest I do?