For newer Macs released after June 2011, there are better options to boot your system that we spell out here:
Today I helped a customer that recently upgraded from Drive Genius 2 to Drive Genius 3. He was wondering how he could burn the Drive Genius 3 startup DVD so that he could use it to Defrag his Mac hard drive. I confirmed that he had an older Mac that was supported by the Boot DVD, as he had a model that was released prior to June 2011. I sent him instructions for burning the DVD to use as a startup disk. I also explained to him that he could use the LiveDefrag instead so that he would not need to restart his computer from an alternate startup drive or the startup DVD to run a Defrag.
During the LiveDefrag, your computer will restart to a minimal system, check your drive for errors and then Defragment your drive. Then when the Defrag completes your computer will restart normally. He was very impressed with this feature and he was able to run the LiveDefrag to optimize his Mac hard drive.