Backing up properly: the 3-2-1 rule for normal people

The distinction sounds pedantic until the day it is not. A sync service exists to make every copy look the same. A backup exists to make one copy look like the past. When a file is deleted, corrupted, or encrypted by something malicious, the sync dutifully propagates the damage and the backup is the only thing that saves you.

The good news is that the standard advice is genuinely simple, has not changed in decades, and can be set up in an afternoon.

The short answer

• Three copies of anything you cannot lose, on two different kinds of storage, with one of them somewhere else.
• Sync is not one of the three. It is a convenience, and it copies mistakes at the speed of light.
• Unplug the drive when it is not backing up. The UK's NCSC is explicit that backup storage should not stay connected, because malware also affects connected devices.
• Phone cloud backup covers most but not all of a phone, and what it covers depends on which services you already sync.
• A backup you have never restored from is a hypothesis. Test one file.

Sync is not backup

iCloud Drive, Google Drive, OneDrive and Dropbox are synchronisation services. Their job is to make the same folder appear identically on every device. If you delete a folder on your laptop, it disappears from your phone. If a file becomes corrupted, the corrupted version is what gets propagated.

Most of them do keep deleted files in a bin for a period, and some keep version history — which is a real, useful safety net, and worth knowing the limits of. But it is a limited window, it usually applies per file rather than to a whole disaster, and it is not designed for the case where the device itself is gone.

A sync answers "where is my file?". A backup answers "what did my files look like on Tuesday?"

What 3-2-1 actually means

The rule is old, unglamorous and still the standard for a reason: each number defends against a different kind of failure.

Translated into an ordinary home: the files on your laptop are copy one. An external drive you connect periodically is copy two, on a different kind of storage. A cloud backup service is copy three, in a different building. That is it — the entire rule, satisfied with one purchase and one subscription.

Your phone: what the cloud keeps

Phone backup is mostly solved, provided you understand the division of labour. Apple's own documentation is clear that iCloud Backup covers device settings, Home Screen layout and app organisation, app data, purchased ringtones, and Apple Watch backups — but explicitly does not re-cover data that is already synced separately through iCloud Photos, iCloud Drive, Notes or Messages in iCloud, because those live in iCloud already.

That design is sensible and it produces one specific trap: the parts covered by sync rather than backup inherit sync's weakness. Photos deleted from iCloud Photos are deleted everywhere, recoverable only from the Recently Deleted album for a limited period. Android with Google Photos behaves the same way.

Your laptop: the two-part setup

Both major operating systems include a competent backup tool, and both are usually switched off.

The important distinction in that table is the first row. A versioned local backup lets you recover a document as it was three weeks ago, which is what you need after the slow-motion disasters — the corrupted project file, the accidental overwrite, the change you made and cannot undo. Sync cannot do that job.

Why an always-connected drive is half a backup

Leaving the backup drive permanently attached is convenient, and it is also how a single event takes both copies. Ransomware encrypts every drive it can reach, including the one plugged into the USB port. A power surge or a failing power supply does not care which drive is the backup.

The NCSC's small-business guidance is direct on this: backup storage devices should not stay connected to the device when not in use, because some viruses also affect devices connected to an infected computer. The same guidance recommends using online and a physical storage device — two backups, in case one is lost, stolen or fails.

The practical version for a household is a drive that lives in a drawer, connected once a week or once a month. A backup that is slightly out of date beats one that was encrypted alongside the original.

The test almost nobody runs

Every piece of official backup guidance ends with the same instruction, and it is the one everyone skips: confirm you know how to restore, and check that the backup contains what you think it does.

This does not need to be an ordeal. Pick one file you would hate to lose, delete your local copy of it (or rename it), and recover it from the backup. Ten minutes, once. What that exercise typically reveals is not a broken backup but a scope problem — an entire folder that was never included because it lives outside the default location, or an external drive full of photos that the backup was never configured to see.

A plan you can set up this weekend

1. List what is irreplaceable. For most households: photos, documents, and anything to do with the tax authorities. Everything else can be reinstalled or re-bought.
2. Buy one external drive at roughly twice the size of the data you are protecting, so versions have room to accumulate.
3. Turn on the built-in backup tool — Time Machine or File History — and point it at that drive.
4. Add one offsite copy. A cloud backup subscription, or a second drive kept at a relative's house and swapped occasionally.
5. Unplug the drive between backups and put it somewhere that is not on top of the computer.
6. Export your photo library once a year to that drive, in full.
7. Restore one file and put a reminder in the calendar to do it again in twelve months.

None of this is clever, and that is the point. Backup is the one area of consumer technology where the boring, twenty-year-old advice is still exactly right, and where the only real failure mode is not getting round to it.

Sources

• NCSC — Backing up your data
• Apple Support — What does iCloud back up?
• CISA — Data backup options