3-2-1 backups

Keep 3 copies of anything that matters, on 2 different media, with 1 off-site.

Why it works

Each rule breaks a different failure mode: device loss, media-type failure, and site-level disasters (fire, theft, flood).

More in Computers

• 2¹⁰ ≈ 10³Every 10 bits multiplies by ~1,000 — kibi and kilo differ by just 2.4%.
• Each subnet bit halves the hostsEvery bit moved from host to network halves the addresses — a /24 has 254 usable.
• RAID is not a backupRAID protects against disk failure — deletion, ransomware and fat fingers replicate instantly.
• The ×100 latency ladderRAM ~100 ns, SSD ~100 µs, spinning disk ~10 ms — each rung roughly 100× slower.

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