Know It Cold — SREF

The SREF is closed-book: no tab to flip to, no glossary open beside you, nothing but what's already in your head when the sixty-minute clock starts. This page is the last-mile crib list for that specific constraint — not a re-teach of the eight modules, which the rest of this course's SREF shelf already covers in full, but the small set of facts you need to be able to produce instantly and without deliberation: the eight module names in the order DevOps Institute lists them, the exact format numbers, the error-budget arithmetic worked against real window sizes, and the handful of term-pairs that single-best-answer questions are built to exploit. Read it once for shape. Then close it, recite it, and check yourself — reading this page a second time feels like studying and mostly isn't.

How to use this page

☺ Like you're 10: Don't just read it — cover it, say it out loud from memory, then peek and see what you missed.

Every section below is written to be recited, not skimmed. The honest way to use this page: read one section, close your eyes or cover the screen, say the whole thing back out loud or on a scrap of paper, then check what you got wrong. What you get wrong the first time is your actual study list — it will be shorter than you expect, and far more specific than "I should review the whole thing again." Anything you miss twice belongs on a flashcard in the flashcards, not on a third read of this page.

The exam format — say it without looking

☺ Like you're 10: Five numbers, memorized cold: how many questions, how long you get, what score you need, how many that actually is, and how many topics it's drawn from.

These numbers should be reflexive before you sit down — not because you'll be tested on them directly, but because pacing depends on them. Full logistics, registration, and cost live on the SREF exam page; this is the compressed version you carry into the room.

The eight blueprint modules, in order — with a mnemonic

☺ Like you're 10: Eight topics, always in this order — and one silly sentence makes them stick without any effort.

DevOps Institute lists the SREF blueprint as eight modules. You don't need to recite them in order for the exam itself — questions aren't grouped by module — but having the full set cold means you never blank on "which module was that in" while triaging a hard question, and it means you can audit your own prep against all eight instead of accidentally skipping one. First letters spell a sentence worth memorizing outright:

The error-budget formula — worked cold, every window size

☺ Like you're 10: One formula, and four numbers about how many minutes are in a day, a week, a month, and a quarter — memorize both and you can answer almost any error-budget question on the spot.

This is the one calculation the SREF is likely to ask you to actually perform, in some form, and it only takes two things memorized cold: the formula, and how many minutes live inside whatever window the question gives you. Full derivation and the "burning vs. banking" policy are on SLIs, SLOs & error budgets; this is the arithmetic stripped down to what you recite.

Error budget = (100% − SLO) × window, expressed in the window's own units

Step 1: convert the window to minutes
Step 2: subtract the SLO from 100% to get the allowed failure rate
Step 3: multiply

Cross those against the SLO and you get the standard "nines" table — the single most quotable set of numbers in the whole discipline, and exactly the shape of fact a closed-book exam rewards having memorized rather than derived under pressure:

Notice the pattern that makes this table reconstructible even if you blank on one cell: each additional nine divides the allowed downtime by roughly 10x. If you remember 99.9% → 43.2 minutes a month, you can derive 99.99% by dividing by ten (≈4.32 min) and 99% by multiplying by ten (≈432 min = 7.2 hours) without memorizing every row separately.

The trap-question term pairs — cold

☺ Like you're 10: Most wrong answers on a test like this aren't from not knowing the topic — they're from mixing up two words that sound almost the same. Here's the exact one-line test for each pair that trips people up.

Single-best-answer questions are built around near-miss pairs: two terms that sound related, where only one is actually correct for the question asked. The fix isn't studying harder in general — it's having the exact distinguishing sentence for each pair ready to fire, so a distractor built around the wrong half of the pair stops working on you. These are pulled directly from where this course's SREF shelf covers them; follow the links if any one of these feels shaky rather than solid.

A smaller set worth having cold too, even though they sit more at the edges of the eight-module blueprint than at its center — closed-book questions still lean on this vocabulary when a scenario needs a concrete resilience mechanism named correctly:

• Circuit breaker states: Closed (normal — calls pass, failures counted) → Open (calls fail instantly, no network attempt, cooldown running) → Half-open (a few test calls decide: close again, or reopen). See reliability patterns.
• Load test vs. stress test vs. soak test: Load test confirms targets hold at expected traffic. Stress test pushes past expected traffic to find the actual breaking point. Soak test holds elevated traffic for hours to catch slow leaks a short burst test would miss. See capacity planning & performance.
• Horizontal vs. vertical scaling: Vertical = bigger box, simple, hard ceiling, still one point of failure. Horizontal = more boxes, effectively no ceiling, improves availability, adds distributed-systems complexity.

That's the full crib sheet — five format numbers, eight modules behind one mnemonic sentence, one formula plus the minutes to run it against any window, and the term-pairs a single-best-answer question is built to exploit. Pair it with the SREF Concept Reference for definitions in full, Closed-Book Strategy — No Docs Map for exam-day tactics, and Answer Triage — SREF for practice spotting exactly these distractors in context. Then test the recall for real against the practice bank and a timed full mock exam before you book the sitting described on the exam guide.