One long-standing and useful feature in OS X is its ability to boot from practically any mountable partition, including external drives. This allows for quick ways to test an installation, isolate different uses of your Mac to separate boot drives, troubleshoot aspects of your Mac’s hardware and internal storage, and create bootable backups of your Mac’s hard drive. While useful, there are times when your Mac will not boot to such partitions, even if they are perfectly healthy. If so, then here is what to do about it. Continue reading →