Hi, I am working on a dual 1ghz Quicksilver with 5 internal hard disk drives. It was purchased used like this from a media company. It worked fine for a long time, but recently some of the drives have been inconsistant in mounting at startup. Here's what I know: The four hard drives which are affected all share a controller card - two sets of master/slave, configured correctly. They are labeled: A,B,C,D. Of these drives, it was usually the D drive which wouldn't mount and sometimes the C. To my knowledge, the A & B drives weren't failing to mount. C & D share a bus on the controller card. There's another disk on the system's built-in controller, which has not failed to mount. This is the startup volume. The first thing I did was reset the reset the PMU. After that, all of the drives mounted and I rebooted several times to be sure. After that I rebuilt the directories of the drives with Diskwarrior, which found and repaired a fair amount of errors. For a day or two, all the drives mounted fine, but then they went back to the same pattern. The next thing I did was switch the position of the two sets of drives on the controller card to see if the problem followed them. The result was that C & D still failed occasionally in their new position and A & B still mounted. This made me suspect the controller card less and the cable more. So I replaced the cable on C & D. For the first few boots, C & D mounted fine. But then A didn't mount once and C & D went back to their flakiness. At this point I am not sure whether to suspect the controller card or maybe the power supply, which is probably under some strain to be powering 5 hard drives, the controller card, superdrive, etc. 1. Could a strained or failing power supply act like this? 2. Otherwise, is the controller card failing? 3. Could the startup volume, which always mounts, somehow be the cause of the problem? If you've even read this far I thank you! Any advice about how to further test to nail this down would be greatly appreciated.