Big disks want dual parity

Beyond ~4 large drives, prefer RAID 6 over RAID 5 — rebuilds are when second failures strike.

Why it works

A rebuild reads every sector of every surviving disk for hours under stress. With multi-TB drives, the odds of hitting an unrecoverable error mid-rebuild stop being negligible.

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.
• RAID is not a backupRAID protects against disk failure — deletion, ransomware and fat fingers replicate instantly.
• 3-2-1 backupsKeep 3 copies of anything that matters, on 2 different media, with 1 off-site.

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