You get 2GB of storage space with Dropbox, gratis. If you don't have much in the way of photos and documents to back up, that may be plenty. (If you do need more space, you can pay $99 per year for 50GB.) Move your important documents and photos to the Dropbox folder, and the service will automatically sync them to Dropbox's servers on its own. If your hard drive goes belly up, you can simply install Dropbox again on your replacement, and the service will automatically download all your synced files.
Installing Dropbox, and keeping your most important files there, can take mere minutes. And as long as you ensure that you save your important data to that folder, you're golden. But if you're willing to spend a little more time and a little more cash, there are other approaches that can back you up even more completely.
Next easiest plan: Time Machine
As you probably know, you have impressive backup software built into your Mac, for free. But if you never configure Time Machine, then it can't help you. The good news is, configuring Time Machine to back up your computer takes just a bit of time.
- Buy or acquire an extra hard drive. (See our buying guides for external hard drives and for portable hard drives.) This is ridiculously cheap at this point; you can get at least a terabyte of storage space for less than $100. All you need is a drive that works with your Mac; USB drives are still the most affordable; Thunderbolt drives will likely be faster.
- Connect the drive to your Mac.
Most of the time, Lion should ask you whether you'd like to use the newly-connected hard drive for Time Machine backups. Say yes, and your Mac will automatically back up your files to the drive as needed. It's great, and it's mostly painless. If you've bought a big enough drive, you'll have a copy of everything in case of emergency. Time Machine stores incremental backups of your data in time-based snapshots. So if you updated your big presentation for work yesterday, and realize today that in fact you screwed everything up, you can use Time Machine to step back to an earlier version of that file. And you can recover the file if you accidentally delete it, too.
Time Machine's smart enough to only back up data that's changed; that way, instead of recopying the complete contents of your hard drive each time your Mac starts a new backup, only the updated and new files are transferred. In your main drive fails, your latest Time Machine backup should contain a nearly up-to-the-minute snapshot of how everything looked before the crash. And unlike Dropbox, Time Machine backs up pretty much everything on your Mac--you don't need to make sure you're putting all your important stuff in a single folder.
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