I'm somewhat paranoid about backing up my data files. And by "somewhat paranoid," I mean "petrified." If you're not of a similar mindset, you should be. Consider what it would mean to lose some irreplaceable photos, for instance. Or the please-let-me-keep-my-job presentation that you've been pulling together for months. Or your financial data. Being paranoid in every waking hour isn't a great way to get through life, but when it comes to backing up your data it's nearly impossible to go too far. Here's the multi-level plan I use to keep my paranoia at bay.
Level 0: System Setup
My backup plan begins with my basic system setup, which may be different from yours. I keep very little data on the internal boot drive. My user's folder is on that drive, along with my most-used applications. But that's it; everything else is saved elsewhere. I even go so far as to use aliases (or symbolic links, if necessary) to move large data files off the boot drive for programs that don't let me specify a storage location. As a result, my boot drive is typically fairly empty — I'm using just 75GB of the 256GB SSD in my Retina iMac, for example.
So where does everything else reside? On an external RAID seftup, complete with a spare drive in a drawer (in the event of a drive failure). This strategy protects my files well enough while I'm working. But as you'll often hear, RAID is not a backup solution. So how then do I back up my files?
I use a multi-drive, multi-location backup strategy, with the goal of ensuring that I won't ever lose a critical file due to equipment failure or natural disaster. (It's still quite possible to lose data via user stupidity; even the best backup plan isn't completely foolproof in that regard. But I take steps to minimize that risk as well.)
Level 1: Time Machine
Time Machine is my first line of defense, and the only aspect of my strategy that includes support for older versions of files. It's the first place I go if I've accidentally deleted a file (user stupidity), or need an older version of something.
In order to keep the deepest version history possible, I skip a fair number of file types from my backups. You can have Time Machine skip certain files or folders by clicking the Options button in the Time Machine system preferences panel, then clicking the plus sign to adding those files you'd like Time Machine to skip.
Tip: If you add an OS X-owned folder — such as the top-level System folder — Time Machine will ask you if you'd like to skip all system files. I reply yes, because Level Two of my strategy takes care of my system files. When you say yes, Time Machine shows "System Files and Applications" as being excluded from the backup.
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