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Lesson 8 of 8 · 6 min · +100 XP

What is the 3-2-1 backup rule?

The 3-2-1 backup rule says to keep three copies of your data, on two different kinds of storage, with one copy offline or offsite. If a drive fails, a laptop is stolen or ransomware encrypts everything connected, one copy survives. Test it by restoring a file now and then, because a backup you have never restored may not work.

▶ Try it

Why it matters

Keep three copies, on two kinds of media, with one offline or offsite. Ransomware also encrypts anything still attached, so only a disconnected copy guarantees recovery.

In 6 minutes you'll be able to

  • Keep 3 copies, on 2 kinds of storage, with 1 offline or offsite.
  • Sync is not backup. Choose a backup that keeps old versions.
  • Test a restore now and then, so you know it works.

What you'll practise

  1. 3-2-1, explained

    Three numbers, one rule, plus the step most people skip.

    3️⃣ 3 copies
    Your original plus two backups. One copy can fail, and you still have two.
    2️⃣ 2 kinds of storage
    For example your laptop and an external drive. One fault won't hit both.
    1️⃣ 1 offline or offsite
    Unplugged, in another place, or in a cloud backup that keeps old versions. Ransomware can't reach it.
    ✅ Test the restore
    Now and then, bring one file back from the backup. Then you know it works.

  2. Is it really a backup?

    Sort each setup. Would it survive a dead laptop or a ransomware attack?

    • An external drive you unplug after each backup → Real backup
    • A second folder on the same laptop → Not a backup
    • A synced cloud folder that mirrors every change instantly → Not a backup
    • A cloud backup that keeps older versions for 30 days → Real backup
    • A USB drive that is always plugged in → Not a backup
    • A copy of your photos kept at a family member's home → Real backup

  3. Ransomware strikes

    Ransomware hits four NovaCorp colleagues at home. Whose backup plan saves them?

    1. Priya backs up to a USB drive that stays plugged into her laptop. Is she safe?

      • No, the drive gets encrypted too (Answer)
      • Yes, she has two copies

    2. Leo's backup runs every Friday, but he has never tried restoring from it. Is he safe?

      • Maybe, he can't know until he tests it (Answer)
      • Yes, the backup runs every week

    3. Sam has her laptop, a cloud backup with version history, and a drive in a drawer. Is she safe?

      • Yes, that's 3-2-1 (Answer)
      • No, ransomware reaches everything

    4. Ravi's files are encrypted. He has no backup. A note demands payment. What should he do?

      • Disconnect, report it, and get expert help before deciding anything (Answer)
      • Pay quickly before the price goes up

Remember

A backup you have never restored is a hope, not a backup.

Key facts

  • The 3-2-1 rule was recommended in the US government paper Data Backup Options: keep 3 copies, on 2 different media, with 1 copy offsite. · Source: US-CERT, Data Backup Options (2012)
  • CISA advises keeping offline, encrypted backups and testing them regularly, because ransomware attackers look for reachable backups to delete or encrypt. · Source: CISA, #StopRansomware Guide (2023)
  • Cloud-synced copies can be overwritten once local files are encrypted, so sync alone is not a backup. · Source: CISA, #StopRansomware Guide (2023)
  • In Verizon's 2025 report, 64% of ransomware victims did not pay the ransom, and the median payment fell to $115,000. · Source: Verizon, 2025 Data Breach Investigations Report

Updated:

Questions people ask

How often should I back up my data?

As often as you can stand to lose the work in between. For most people, an automatic daily or continuous backup plus a weekly offline copy works well.

Is cloud storage the same as a backup?

Not always. A synced folder copies deletions and encrypted files too. A real cloud backup keeps older versions, so you can roll back to a point before something went wrong.

Does the 3-2-1 rule still work against ransomware?

Yes, as long as one copy is truly offline or can't be changed. Some people extend it to 3-2-1-1-0: one copy offline or immutable, and zero errors in test restores.

What is the easiest way to back up a home computer?

Turn on your computer's built-in backup to an external drive and unplug the drive afterwards. Add a cloud backup service that keeps old versions, and you have 3-2-1.

Related terms