There are two Applications here I can recommend you to do backup for your Mac, one is Carbon Copy Cloner 3.0 and the other one is SuperDuper!

Backup? For Mac? Why?

We all know that Mac is far more secure than 'you-know-what-I-mean'. However, in this world nothing is perfect, including your Mac. Somehow, sometimes, somewhere or somewhat, your Mac will get a glitch of error and mess up all of your data storage. Instead of crying over the night (under the blanket), it's just more than good to do backup. But it's essential yet not compulsory.

Carbon Copy Cloner

Also known as CCC. Choose this one if you want to make backup of only some portions of your Disk. It also gives us the forecast what should we get if we proceed further.

For further understanding and sea of feedbacks from it's experienced user, you can refer to its site: Carbon Copy Cloner 3.0 and Mac

SuperDuper!

SuperDuper! is very good at cloning your whole Mac HD, as it can give you high level of compression when cloning and I love its friendliness to its user.

In its site, there is full explanation how to use it, I will give you the link. Here is the link to there: SuperDuper! for Mac