One copy is the original, and two backups means a single failure or even a double failure does not wipe you out. More copies means more chances to recover when something goes wrong.

Does the offsite copy have to be cloud?

No. Offsite just means not in the same building. Cloud storage works, but so does a drive kept at a friend or family member's house. The point is surviving a fire, flood or theft at home.

What Is the 3-2-1 Backup Rule (and How to Use It)?

Q: What is the 3-2-1 backup rule?

Keep three copies of your data, on two different types of media, with one copy stored offsite. It is the simple, battle-tested standard that protects against drive failure, theft, fire and ransomware all at once.

Published: July 12, 2026

Live answer · Amazon.com

Pulling live prices…

📊 As of October 23, 2026, the typical external drive (4TB+) on Amazon.com is $52/TB or $0.052/GB, widest choice around $34.84/TB, with some as cheap as $23.57/TB across 518 live listings.

Sourced from real discussions on r/DataHoarder, r/backup and r/homelab, cross-checked against live PricePerGig listings.

The 3, 2, 1 backup rule is your safety net to never lose data, by simply having three copies of data, on two different types of media, and at least one backup somewhere else. The best thing you can do is put your old drives to use as backups that you leave at a friend or relative’s house. If you’re concerned about them reading the data, you can use BitLocker or other full drive encryption methods.

The table above shows live external drive prices on your marketplace, because building proper backups means owning a few good drives, and they are cheaper than you think.

The rule, broken down

Let me unpack each number, because each one defends against something different.

Three copies. The original plus two backups. One backup is good, two is safe.
Two types of media. Not all eggs in one basket. For example an internal drive plus an external drive, or a NAS plus the cloud.
One offsite. At least one copy lives somewhere else entirely, so a house fire or burglary cannot take everything.

Hit all three and you are protected against nearly everything that destroys data.

Why each part matters

Each number is there for a reason, and skipping one leaves a hole.

Three copies protects you when a drive dies, which they all eventually do.

Two types of media protects you when a whole class of thing fails, like one dodgy batch of drives or one corrupted system.

One offsite copy is the hero. It is the one that survives the fire, the flood, the theft and the ransomware that encrypts everything in your house at once.

Miss the offsite copy and a single bad day can erase years of memories.

A simple real world setup

You do not need anything fancy. Here is a setup most people can build.

Copy one: the data on your computer or NAS. The original.
Copy two: a local backup on a separate external drive or a second box.
Copy three: an offsite copy, either cloud storage or a drive kept at a relative’s house.

Buy the drives for it using the live table above, chasing the best price per TB. Storage is cheap. Your photos and files are not.

Where RAID fits in

Quick myth bust, because people get this wrong constantly.

RAID is not a backup. It keeps a machine running when a drive dies, but it does not protect against deletion, ransomware or theft.

So RAID can be part of copy one, giving you uptime, but it never counts as your second or third copy. We explain why in detail in is RAID a backup.

The bottom line

The 3-2-1 backup rule is three copies, on two types of media, with one kept offsite. It is the simplest plan that actually protects you from every common way data gets lost.

Build it with cheap drives from the live table above, make sure that offsite copy genuinely exists, and you will never have that sick feeling of losing everything. It is the cheapest insurance you’ll ever buy.

Remember, RAID is not a backup, and the simplest thing you can do right now is use an old drive to make a copy of your data, or buy an external drive just to have that one extra copy of the most important data, even if you can’t back it all up, just the most important.

The rule, broken down

Why each part matters

A simple real world setup

Where RAID fits in

The bottom line

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