The 3-2-1 rule: backups that actually protect your data
A backup on the same server as the original data isn't a backup, it's a copy. The simple principle that tells the two apart.
The 3-2-1 rule predates the cloud but remains the reference standard: 3 copies of the data, on 2 different media, with 1 off-site.
Why 3 copies
The original data plus a single copy doesn't survive corruption that hits both at once (a sync error, for instance). Three independent copies drastically reduce the odds that one incident wipes out everything.
Why 2 different media
A disk and a cloud backup, for example — not two identical disks in the same array. The goal is that a failure specific to one technology (a bad batch of drives, a software bug) doesn't hit every copy.
Why 1 copy off-site
This is the most commonly neglected point, and the most critical: a fire, water damage, or ransomware that encrypts everything reachable from the local network must not be able to reach the backup copy.
What we test, not just what we configure
A backup that's never been restored isn't a reliable backup, it's a hope. As part of IT Packs, we systematically schedule a quarterly restore test, off the production server — that's what distinguishes a backup from a mere copy.
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