RAID is not a backup

RAID protects against disk failure — deletion, ransomware and fat fingers replicate instantly.

Why it works

Redundancy keeps the array serving through hardware faults. It faithfully mirrors every mistake, too. Different threat, different tool.

Do it exactly

Estimate with the rule, then check it against the calculator that models it properly.

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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.
• 3-2-1 backupsKeep 3 copies of anything that matters, on 2 different media, with 1 off-site.
• The ×100 latency ladderRAM ~100 ns, SSD ~100 µs, spinning disk ~10 ms — each rung roughly 100× slower.

Browse all 96 rules of thumb →