We knew from previous reports that Thunderbolt would support Target Disk Mode but there was some doubt whether we would be able to boot from external drives using a Thunderbolt connection. Now, Anandtech has already received their 12TB Promise RAID system with Thunderbolt support and has confirmed that you can boot from the drive, reports Macrumors.
Target Disk Mode allows you to use your Mac as an external drive, connected to another computer. This can be useful if an OS X installation becomes unusable, allowing you to copy files off of the unbootable computer in preparation for a reinstall. In an article about the new MacBooks with Thunderbolt support, Andy Ihnatko confirmed that Target Disk Mode would be supported, but said that booting would not be.
Anandtech, who has received one of the first RAID setups with support for the new connector, has gotten it installed and confirmed in a Tweet that you can boot from it. The image above is of their 12 TB Promise unit. This is nice to know as many Mac users keep a bootable backup of their computers on an external drive using tools like Super Duper. Being able to boot from an external drive means that you can have your system up and running in minutes if something were to happen to your main drive.