Hi, This is a long post - but one that I hope someone can offer advice on. The Hardware Hackintosh running OSX 10.8 (but this has happened on all versions of the OS i.e. 10.6/.7 etc) 3 x Internal SATA Hard Drives - All working perfectly. External Drives: 2 x Western Digital My Book 1TB USB Hard Drives 1 x Seagate 750GB Hard Drive with USB2 connectivity 2 x IcyBox Dual Bay USB2 hard Drive enclosures using JMicron Chipsets - these enclosures have 2 x 1TB Western Digital Green in each (totaling 4 TB across the 2 enclosures). D-Link 7 Port USB2 Hub The Problem - USB Hard Drives connected to the Mac are ejected from the system without notice and at random times AND/OR - The external hard drive remains mounted, but when trying to write to the drive/partitions, Finder throws an error message up saying the operation cannot be completed - error code -50. - Time Machine:* TM will back up successfully several times, before eventually throwing an error up that it cannot create the folders required on the drive. - The only way to be able to use the drives again is either remount the drive, or in some case, it is required to completely power the drive down and then reconnect. Re-creating the problem I have honestly not found a sure-fire way of replicating the problem.* It seems completely random.* It happens when I am actually sat at the computer, but it also happens when I am away from the computer.* In the past - my Time Machine hard drive has been one of the Western Digital MyBook drives.* I also used the second MyBook for SuperDuper backups (extra redundancy).* The 4TB drives in the IcyBox enclosures have been used to backup my ripped movie collection. Recently however - I decided to have 2 of the 1TB drives in the IcyBox enclosures to be TM and SuperDuper backups.* I have however reverted TM back to one of the Western Digital drives, purely for testing purposes.* SuperDuper is backing up to one of the 1TB drives in the IcyBox. I am trying various things to see if I can find the issue, but it is such a random event that it is taking ages to even come close to find a problem.* Sometimes the drives will stay active for a few days, sometimes only a few hours, even minutes. Theories I have several theories as to why my USB drives continually disconnect. 1.* The D-Link USB Hub. Could connecting the drives through the hub be causing the problem? I don't really see how, unless it is a documented case that D-Link USB hubs do not play nice with OSX? To try and rule this out I have connected the current Time Machine back up drive (Western Digital MyBook) directly to the USB port on the back of the computer. The SuperDuper (IcyBox enclosure) drive is currently connected through the D-Link hub. I have removed all the other drives from the enclosures - so at present I have only 2 external drives connected (1 x 1TB Western Digital MyBook, 1 x 1TB Western Digital Green inside one of the IcyBox dual-bay enclosures - connected through D-Link Hub). 2. JMicron Chipset I have done a bit of research on the internet and there are a few indications that perhaps JMicron SATA-to-USB controller chipsets found in a lot of external hard drive enclosures (including the dual bay IcyBox external enclosures that I have) do not play nice with OSX. If the JMicron chipsets in the 2 IcyBox enclosures is a problem - would that cause issues with other USB devices on the USB bus off the Mac? (i.e. can the JMicron chipset in the enclosures cause devices such as the WD MyBook drives which I assume use a non-JMicron chipset, to experience similar failures?) 3. Green Hard Drives As I have said, I have 4 Western Digital Green 1TB hard drives inside the IcyBox Dual Bay Enclosures. Could the fact that these drives are 'Green' be causing a problem? They do go to sleep after x number of minutes, but they do wake up when required. But could on the occasion when I have problems, could this be caused by the 'Green' feature interrupting OSX in waking the drives? Coupled with JMicron chipset, could this be compounding the issue? Possible Solutions I am prepared to spend money on replacement drives and/or enclosures etc - but I would hate to spend x amount of money and have the same problem. So I am hoping to get some advice on what drives/enclosures are more than likely to work flawlessly with OSX. Thanks for reading!