This problem suddenly started happening, and I'm not sure why. The computer goes completely unresponsive. I did not upgrade Mac OS X nor modify any other configuration between several successful boots and then now. If I take the time-machine drive out, the computer boots just fine. I've taken the time-machine drive out, hooked it up to my laptop via USB, have verified the disk, checked partition tables, etc. It reads fine, no signs of drive failure. If I boot with both drives in, even with a USB stick, then the same failure occurs. My hunch is there is a bug in Chimera in which the software encounters some unexpected state, doesn't know how to handle it, and freezes. I'm happy to provide any logs or try any custom Chimera builds to help diagnose the problem, I just don't know where to start. In a few days, I'm going to try re-partitioning the drive to see if it changes things, but hopefully I can use the reproducible state to help diagnose a Chimera issue. Thanks!