# Backup

> A separate copy of your data, kept so you can get it back when the original is lost.

- Level: Basic
- Topics: Data, Security
- URL: https://tidbit.legios.com.ar/backup/
- In Spanish: [Copia de seguridad](https://tidbit.legios.com.ar/es/backup/)

A **backup** is a copy of data stored separately from the original, so it can be restored if something goes wrong: a laptop is stolen, a disk dies, someone deletes the wrong folder, a fire hits the office, or ransomware encrypts every file. It sounds obvious, but many people only discover their backups were missing, incomplete or impossible to restore on the day they need them.

A widely used guideline is the **3-2-1 rule**: keep at least **3** copies of your data (the original and two backups), on **2** different kinds of storage (say, the laptop and an external drive or a cloud service), with **1** copy off-site, in another building or another region. Each part protects against a different failure: one copy can break, one kind of media can fail, one place can burn. Many teams now add that one copy should be offline or **immutable**, impossible to change or delete for a while, because modern ransomware hunts for backups it can reach.

A sync service is not a backup by itself: if you delete or corrupt a file, the change is copied everywhere within seconds. Real backups keep older versions, so you can go back to how things were last Tuesday. And a backup only counts if it can be restored, so testing a restore every so often is part of the job.

## An analogy

Keeping photocopies of your passport: one in your suitcase, one in your email and one with a relative at home. Lose your bag on a trip and you still have proof of who you are.

## Keep in mind

- A separate copy that lets you restore data after loss, damage or deletion.
- 3-2-1: three copies, two kinds of storage, one copy off-site.
- Keep at least one copy offline or immutable as protection against ransomware.
- Sync is not backup; keep old versions and test that restores work.

## Go deeper

- [Data backup options (CISA, PDF)](https://www.cisa.gov/sites/default/files/publications/data_backup_options.pdf)
- [The 3-2-1 backup strategy (Backblaze)](https://www.backblaze.com/blog/the-3-2-1-backup-strategy/)
- [Backup on Wikipedia](https://en.wikipedia.org/wiki/Backup)

## Related terms

- [Malware and ransomware](https://tidbit.legios.com.ar/malware-and-ransomware/): Software built to harm you; ransomware locks your files and charges to unlock them.
- [Cloud computing](https://tidbit.legios.com.ar/cloud-computing/): Renting computers over the internet instead of buying your own.
- [Regions and Availability Zones](https://tidbit.legios.com.ar/regions-and-availability-zones/): Where AWS physically lives: cities worldwide, each split into separate data centers.