I recently followed a discussion on booting from a Time Machine volume. One participant was 100% sure that when the Time Machine volume did not contain a separate, bootable partition, booting from the volume was not possible. This is wrong. Misunderstanding this might have big consequences, after all we are talking about backups here.

The OSX bootloader supports booting from files, when the file is stored in a known filesystem, i.e. the bootloader must understand the filesystem.  This file is then handled as a partition containing a filesystem.

Time Machine stores OSX’s hidden recovery partition as a file on the Time Machine volume. When running Time Machine for the first time, a logmessage conforming the above action is generated.

A tool like Carbon Copy Cloner can create and manage this file, so you can verify the file is there. One should always test any recovery mechanism. If you don’t, you might be forced to test it after a failure, and every IT-pro knows that this is where painful news articles are created…