One copy of your files on one drive is a single point of failure. And sooner or later, single points of failure fail.
Odds are you’ve built up years of photos, videos, financial records and maybe some personal poetry you’d rather nobody read. Making sure all of it is backed up isn’t a fun way to spend an afternoon. But you know the feeling of finding out important files are gone for good, and it’s much worse.
The good news is that a dead hard drive doesn’t have to end with you breathing into a paper bag. There’s an old, simple rule for this, and it still holds up.
Three copies, two types of media, one offsite
The 3-2-1 rule tells you how many copies of your data to keep, how many types of media to spread them across and where that media should be. Keep three copies of your data on two types of media, and store one of those copies offsite. These days “two types of media” usually gets read as two different devices.
Photographer Peter Krogh popularized the rule in his 2009 book, “The DAM Book: Digital Asset Management for Photographers.” It was written for people with huge photo libraries, but the idea works just as well for anyone with a laptop full of tax documents.
Here’s how it plays out. Say your only copy of your vacation photos is on one SSD. If that SSD dies, so do the photos.
Copying them to a few more drives helps, though not as much as you’d hope. If every copy sits in the same house, a flood, house fire or burglary can wipe them all out at once.
The offsite copy fixes that. Ideally it’s far enough away that whatever disaster hits your home can’t also hit the place where that copy lives. The whole rule comes down to redundancy, so losing one copy is annoying instead of catastrophic.
The rule has changed since 2009
Both the tech and the threats have changed a lot since the rule first caught on. You probably aren’t burning many CDs anymore, and people worry less about their storage media going obsolete than they used to.
So people adapt it. You can find plenty of threads on Reddit where careful users explain how they’ve made the 3-2-1 rule fit their own needs and what they can realistically afford. A multinational corporation needs a far more elaborate plan than you do, and that’s fine.
A setup that works for a lot of people looks like this: the original files on your laptop, a second copy on an external hard drive and a third on a private cloud server. That covers three copies, more than one device and an offsite location.
Your cloud sync might not be a backup
Services like iCloud or Google Cloud can count toward the offsite copy, but read the settings first. Depending on the service and how syncing is set up, deleting a file on your computer might delete it from the cloud too. A copy that disappears when the original does isn’t protecting you from much.
Other services back up entire devices automatically. Storage limits and pricing tiers vary, so check what you’d actually get before you sign up.
Security threats have also changed how the rule should be applied. Ransomware is the big one. An offsite copy can still be hit by a ransomware attack if the device it’s on is connected to a network, so being in another location doesn’t make it safe from everything.
Where to start
You don’t need a perfect setup on day one. Pick the folder you’d hate to lose most, whether that’s family photos or last year’s tax returns, and make two more copies of it: one on an external drive you keep at home, and one somewhere outside your house that a deletion on your laptop can’t reach. Once those three copies exist, you’ve started following the 3-2-1 rule, and the cat pictures and haikus will survive the next dead drive.
