Backups that actually work: the 3-2-1 rule in real life

A backup is a separate copy you can go back to. Sync is a mirror that copies whatever happens, including the bad things. If you delete a folder, if an application corrupts a file, or if ransomware encrypts your documents, a sync service faithfully reproduces that across every device within seconds. That is the single most important distinction in this subject, and it is why a cloud drive full of your files is not a backup. The working arrangement is 3-2-1: three copies of anything you care about, on two different kinds of storage, with one of them somewhere else. For a normal household that means the live copy on your devices, an automatic local backup, and an offsite copy that is not simply a mirror.

Why your cloud drive is not a backup

Sync services do protect you from one thing very well: a device dying or being stolen. Your files are elsewhere and you can sign in from another machine. That is real, and it is why sync feels like a backup.

It fails on everything else. Deletion propagates. Overwriting propagates. Encryption by malware propagates, and it propagates fast, because sync clients are designed to push changes immediately. Most services keep deleted items in a trash folder and older versions of files for a limited window, often around thirty days, which helps if you notice quickly and does nothing if you notice in March that something vanished in November.

There is also the account itself. If your account is locked, suspended or taken over, every copy in it becomes unreachable at once. A backup that lives entirely inside one account you might lose access to is not really a second copy, it is the same copy with extra steps.

The 3-2-1 rule in household terms

Three copies, two media, one offsite. Translated into a house with a couple of laptops and some phones, it looks like this.

The live copy is whatever is on your devices right now. That is copy one, and it is the one you should trust least.

The local backup is an external drive attached to the main computer, running the built in backup tool on a schedule: Time Machine on macOS, File History or a full system image on Windows. Local backups are worth having because restoring 400 GB over a home connection takes days, while restoring it from a drive on the desk takes an hour.

The offsite copy is either a cloud backup service that keeps versions, or a second external drive kept somewhere other than your home, at a relative's house or a desk drawer at work, and swapped every month or two. The point of offsite is a category of disaster that takes the whole building: fire, flood, or a burglar carrying away the laptop and the backup drive sitting beside it.

Phones are the piece most people skip. Photo sync to a cloud account handles device loss, but it is still sync, so add a periodic export of the photo library onto the computer that is being backed up properly. That also solves the storage squeeze described in what to delete first when a phone fills up.

Versioning, and why deletion is the enemy

A backup that only mirrors the current state has the same flaw as sync. What you want is version history: the ability to ask for the file as it was last Tuesday, or the folder as it stood before you reorganized it.

When you evaluate any backup arrangement, ask two questions. How far back can I go, and how long does it keep files that no longer exist on the source? Consumer cloud backup services typically keep deleted files for a set retention period, commonly thirty days by default with longer options available. Local tools like Time Machine keep as much history as the drive has room for, thinning older snapshots as it fills. Longer retention costs storage, and for personal documents and photos the extra space is cheap compared with the loss.

The offline copy and ransomware

Ransomware is what turned the offline copy from good practice into the whole point. Modern ransomware deliberately looks for backups, encrypts anything on a connected external drive or a mapped network share, and waits before triggering so that recent backups contain already encrypted files. How that plays out and what to do in the first hour is covered in how ransomware gets in and what to do first, and the wider families of malicious software in the plain English guide to malware.

Two practical defenses. First, physical disconnection: use two external drives, keep one unplugged and preferably out of the house, and swap them on a schedule. A drive in a drawer cannot be encrypted. Second, backups the computer cannot overwrite, which cloud backup services provide under names like immutable storage, object lock or a separate recovery window. The test is simple. If a program running with your account permissions could delete or rewrite the backup, so could ransomware.

If you do get hit, restore only after the machine is clean, following a proper cleanup of an infected computer. Restoring your files onto a still infected machine just feeds them back in.

Encrypting the backup without locking yourself out

A backup drive is a complete copy of your life in a small object that is easy to steal. Encrypt it. Both macOS and Windows offer this on external drives with a checkbox, and backup software usually offers its own encryption for cloud copies.

The trade off is real and worth saying plainly. Strong encryption, especially end to end encryption where the provider holds no key, means nobody can reset it for you. Lose the password or the recovery key and the backup is gone as thoroughly as if it burned. So write the recovery key down and store it away from the drive, or keep it in a password manager that is itself backed up. Decide too who else would need access if something happened to you, which is one of the practical problems set out in what happens to your accounts after you die.

The restore drill nobody does

An untested backup is a belief, not a plan. Backups fail quietly in ordinary ways: the drive filled up months ago, the software has been asking for a password since an update, a folder was never included, or an external drive silently disconnected.

Do a small drill twice a year. Pick three files of different ages, including one from more than a year ago, restore them into a new folder rather than over the originals, and open each one to confirm it is intact. Then check the parts people forget: are your photos in the backup as full resolution files rather than thumbnails, is the email archive included, and are the folders outside your user directory covered.

Once, do the bigger version. Estimate how long a full restore would take, because an offsite copy of 500 GB over a slow upload connection is a multi day event and that changes how much you want kept locally. Check the backup again after any change: a new computer, a new phone, a reorganisation of folders, or a move to a different cloud service.

A weekend plan for a normal household

1. List what would actually hurt to lose. For most households it is photos, documents, tax and financial records, and anything you made yourself. It is a smaller list than you expect.
2. Buy an external drive with at least twice the capacity of the data you are protecting, turn on the built in backup tool, and let it run overnight.
3. Turn on a cloud backup with version history, or set up a second drive to rotate offsite. Decide which you will actually keep doing.
4. Encrypt both, and store the recovery keys somewhere separate from the drives.
5. Export your phone photo library to the computer that is being backed up, then repeat every few months.
6. Put a reminder in the calendar for the restore drill, and another for the drive swap.
7. Before any device leaves your hands, confirm the backup is current and then wipe the device properly.

None of this needs to be finished in one session. A single external drive running an automatic backup tonight already moves you from one copy to two, and that first step removes most of the risk you are carrying. Storage is also the cheapest part of a computer to add later, which is worth remembering when you read the checklist for choosing your next machine.