Backups: the 3-2-1 rule
3 copies, 2 different media, 1 offsite: the 3-2-1 rule so you never lose important data.
The 3-2-1 rule
3 copies of your data (the original + 2 backups) 2 different storage media (e.g. hard drive + cloud) 1 offsite copy (physically elsewhere, or in the cloud)
"2 different media" really means different: two external hard drives aren't enough if both can be destroyed by the same incident (fire, theft, power surge). Combining a local physical medium and a cloud service covers more scenarios.
Why "offsite" is essential
A fire, theft or flood can destroy the original AND a local backup simultaneously if both are in the same place — the offsite copy (cloud, or a drive at a relative's home) protects against exactly this scenario.
Full, incremental, differential backups
| Type | Principle | Advantage |
|---|---|---|
| Full | Copies everything every time | Simple to restore, heavy and slow |
| Incremental | Copies only what changed since the last backup (full or incremental) | Fast and light, more complex to restore |
| Differential | Copies what changed since the last full backup | A trade-off between the two |
Testing your backups
A backup that's never been tested is just an assumption of a backup — periodically restoring a random file from it is the only way to verify it actually works the day you need it.
Thanks for the feedback!