Mac’s are very reliable. The only component that will fail first is either the battery (in a laptop) or the hard drive. If you have a complete hard drive failure and cannot boot into your Mac, you need to create a bootable USB drive that you can use in those rare but annoying moments. This video will walk you through how to set up the drive. The second half of the video is about how to wipe the USB drive if you ever want it back.
Creating A Bootable USB Drive
I wrote about this article a while ago if you want a more textual version of this video please cast your eyes over this article. I do recommend you set up a USB emergency drive as you never know when you may need it. If you can’t watch the video below you can grab it on youtube.