The 3-2-1 Backup Rule
What it is
The 3-2-1 backup rule is a simple plan for making sure your important files survive the thing that eventually goes wrong. It says: keep three copies of any file, store them on two different types of media, and keep one of those copies offsite. The working file on your computer counts as the first copy; the other two are dedicated backups.
It is a checklist, not a product. You can meet it with an external drive and a cloud service, or two drives kept in two buildings. The point is that your data is never sitting in just one place where one accident can erase it.
Time & frequency
About 15 minutes to set up, then automatic; test a restore every few months.
How to do it
- 1List what you would hate to lose: photos, documents, tax records, project files, an export of your password vault. That list is what the rule is protecting.
- 2Count your copies. The live file on your computer is copy one. Aim for three total, meaning the working copy plus two separate backups.
- 3Put the copies on two different media types. For example, your internal drive plus an external USB drive, or an external drive plus a cloud service. Two media types guard against a failure that hits one kind of storage.
- 4Send one copy offsite, away from where you live or work. A reputable cloud backup counts as offsite, and so does an external drive you keep at another location.
- 5Automate it. Set your backup software or cloud sync to run on a schedule so you are not relying on remembering to do it.
- 6Keep at least one copy disconnected or versioned, such as an external drive you unplug or immutable cloud storage. A copy that malware on your live machine cannot reach is a copy it cannot encrypt.
- 7Test a restore. Every few months, open a real file straight from your backup to confirm it actually opens. A backup you have never restored from is only a hope.
Why it works
The rule works by removing single points of failure. One copy on one drive is one bad day away from gone: the drive dies, the laptop is stolen, a file gets overwritten, or ransomware encrypts it. Each additional independent copy has to fail at the same moment for you to actually lose the data, and independent copies rarely fail together.
The 'two media types' part guards against a hazard that targets one kind of storage, and the 'one offsite' part guards against anything that hits a whole location at once, like fire, flood, or theft. Spread across three copies, two media, and two places, the chance that every copy is destroyed in the same event drops sharply.
Common mistakes
- Treating a sync folder as a backup. Live sync copies your deletions and any ransomware encryption to every device instantly. That is mirroring, not a backup. Keep at least one copy that is not continuously synced.
- Keeping every copy in one place. Three drives in one drawer all burn in the same fire. Offsite means a genuinely different location, not a different shelf.
- Never testing a restore. A backup can be silently corrupt or incomplete, and you find out at the worst possible moment. Open a file from it now and then.
- Backing up once and forgetting. Your data changes constantly, so a year-old backup is missing a year of your work. Put it on a schedule.
Practice it now
Set up your first two copies today
You can hit two of the three parts in under ten minutes.
- Pick one folder you would hate to lose and copy it to an external drive or USB stick you own. That is a second copy on a second media type.
- Turn on a reputable cloud backup or sync for that same folder. That is a third copy, and it lives offsite.
- Add a repeating calendar reminder to unplug and store the external drive, and to open a file from a backup next month to confirm it works.
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