Allow me to be hopelessly naive here... I've been a bit lax with my backup routine, and finally decided to do something about my photos. My main Aperture library is 217Gb, and this sits on a 1TB external USB3 disk. Until now, this has been connected to one of the MBA's USB2 ports, and has never given me any real performance problems (when using Aperture). Knowing USB2 is a bit long in the tooth (and slow), I've acquired the following: - Thunderbolt to USB3 adapter - Four port USB3 hub (No external power supply - I suspect I know where this is going) - Two 2TB portable USB 3 disks (Why not? Storage is cheap). All this works perfectly well until I plug a second USB3 hard disk into the hub, at which point both disks start emitting terrifying clicking noises and disappear from Finder. Questions: 1. Is this a power issue, related to the USB hub's lack of an external power source, or is it a limitation of the MacBook/Thunderbolt? 2. Assuming the former, would an externally powered USB3 hub resolve my problem? Other alternatives? I've noticed the Belkin Thunderbolt Dock is getting cheaper. Generally, I'm reluctant to invest in Thunderbolt as I suspect it's going the way of the Dodo.