Most of the time, a single external drive is all you need for simple, effective and easy backup of your important files. With Time Machine and especially the Time Capsule, you can even back up multiple computers wirelessly to the same device. But in a couple edge cases this type of solution doesn't quite hit the mark.
Back when I worked as a professional photographer, I was always running into problems with data storage. The camera technology kept getting better and better, creating larger and more finely detailed images. At the same time, Apple was moving away from spinning disc hard drives towards solid state flash storage. The capacity of new MacBooks was cut by more than half at the same price, and storing everything, before the cloud came around in earnest, became a real challenge.
As a short term solution over the years, I bought more and more external drives, storing my old movies on one, archiving old photos on another. But this got clunky fast, forcing me to carry drives with me when travelling, and running the risk of losing data every time my backpack got jostled or bumped. The fundamental problem with external drives is that anything you put on them isn't backed up, unless you laboriously clone them to another drive and keep them both updated. Only the stuff on my actual computer's hard drive was getting backed up to another drive, and eventually I hit the tipping point where I couldn't store both my music and my photos on my Mac at the same time.
Enter the RAID. If you haven't heard of this acronym before, it stands for Redundant Array of Independent Disks - basically, safety through duplication. It's the same concept as backing up one drive to another, except that rather than having two separate drives, your Mac sees one single volume, made up of a number of drives. These drives are linked together through a number of different "levels" of RAID, each one offering a different mix of redundancy, speed and accessibility.
There are a lot of ways to set up a RAID system, but the easiest plug-and-play solution for me was a Drobo. This standalone box contains some number of internal hard drives and plugs into your Mac as if it were one single disk. I stripped all my external drives of their casings and plugged them in one by one, moving the data off of them into the Drobo system as it slowly gained capacity with each added drive. After a full day of transferring I was set up: my photo library and archival files were off my Mac and backed up automatically every time I made a change. Everything else I kept on my laptop, backed up to a single separate external hard drive.
Years later this system still works great. Though I don't shoot photos nearly as much anymore, I can keep my Mac's 512 GB SSD running lean and mean by moving files I want to keep onto the Drobo, knowing they're safe and accessible whenever I need them.
So: if you're a professional, or just someone with a ton of files and not a lot of space, think about a RAID setup. It might be just the ticket: external storage that backs itself up, accessible anytime. These days you can even get a RAID that shares itself on the internet, so you can access it anywhere like your own personal cloud. Sound awesome? Want one for yourself? Drop us a line - we love geeking out about this stuff. Well, at least I do.