I have about 5 HDDs and 1 SSD.
I have one external HDD with time machine that does it automatically every hour.
I have ANOTHER (NOTE: I do not use the same HDD just in case it fails, I don't want to have all my eggs in one basket) that has a carbon copy clone on it THAT IS BOOTABLE. This HDD is a USB powered pocket drive that I take with me. In case of SSD failure, I can boot off this drive for an emergency as it is my SSD clone.
I then store important documents etc. in my 16GB free Dropbox account so I can access it anywhere. When I say important, I don't mean bank stuff, I just mean documents I use often.
I then have 2 other external HDD's and my optibay drive to store media etc. on.
I figure, I am relatively safe, pending a natural disaster that wipes all my drives out haha!
I have contemplated doing another carbon copy clone of my SSD on one of my other drives, which I will probably do next week or so... that will give me 3 FULL backups (two of which are bootable) if I needed it.
I use time machine to nab single files/folders that I find I need after I deleted or something... then I use the CCC backup as a full restore/bootable drive if I need it.
I'm not sure what else I can do to protect myself, but I make a living on my MBP (I work from home) so a failure of a HDD would be catastrophic for me.... so I do a little overkill.
In all reality having 1 backup is probably good enough.
Also note, I DO NOT have CCC remove files that are not in the same directly as the SSD when it clones.... this way I can use my external USB pocket drive to store media on as well when I go places. Mostly I use it to transfer stuff from my machine to clients machines instead of a jump drive, as it holds MUCH more space. If I had remove things that are not in the same directory, it would remove my "OTHER" folder, which I use to transfer stuff from machine to machine.
My other external HDD I'm going to partition off and clone, making it remove things that are not duplicates so the partition will be a fully up to date clone... the other part of the partition will be media.
The more I sit and think, I'm halfway tempted to clone my externals to other externals hahaha... I'm SOOO afraid of failures. I had one once, without a proper backup, it crippled me and my business for over a week... was one of the worst times in my LIFE! haha.