Apple Releases Thunderbolt Firmware Update v1.2
 

This week Apple released a firmware update v1.2 for Thunderbolt equipped Macs. The update addresses stability issues for target disk mode. It's a small download at only 1.22 MB, but will require a restart. If you have a Mac laptop, be sure to plug it in before you run the update. During the installation, your Mac will restart and the screen will go gray with a status indication bar.

http://www.hardocp.com/news/2013/05/...re_update_v12/