Exercise 1: What Each Number in 3-2-1 Protects Against, and Why Two of Three Isn't Enough — Possible Solution ==================================================================== WHAT EACH NUMBER PROTECTS AGAINST ------------------------------ Per this chapter: "3 copies" protects against "any single copy failing or becoming corrupted"; "2 media types" protects against "a failure mode specific to one media type or format"; "1 offsite" protects against "whole-site disasters - fire, flood, theft, and ... ransomware spreading across a local network." WHY EACH ONE COVERS A DIFFERENT, SPECIFIC FAILURE ------------------------------ These aren't three versions of the same protection - they each guard against a genuinely different cause of loss. Having three copies does nothing if all three are on drives from the same faulty batch (a media-type failure). Having two media types does nothing if both copies sit in the same room that burns down (a site-wide failure). Having one offsite copy does nothing to protect against ordinary single-copy corruption if that's the only backup that exists. WHY MISSING ANY ONE NUMBER LEAVES A REAL, SPECIFIC GAP ------------------------------ Take an organization with 3 copies and 2 media types, but no offsite copy (satisfying "3" and "2," missing "1"). Per this chapter's own worked example, exactly this configuration - technically redundant copies, but all co-located - failed completely to the server-room fire, because nothing about redundancy or media diversity helps when the actual failure mode is "the whole site is gone." Each number closes a door that the other two leave wide open. WHY THIS MEANS 3-2-1 HAS TO BE EVALUATED AS A WHOLE, NOT PARTIALLY ------------------------------ A backup strategy that satisfies two of the three numbers isn't "two thirds safe" - it's fully exposed to whichever specific disaster the missing number was meant to guard against. Since the three numbers protect against different failure modes rather than the same one with diminishing returns, there's no partial credit for satisfying most of the rule. WHY THIS WORKS AS AN ANSWER ------------------------------ It states what each number specifically protects against, explains why they're not redundant with each other, and explains concretely why satisfying only two of the three still leaves the organization fully exposed to the exact disaster the missing number exists to prevent.