Exercise 2: Why 100% %util Doesn't Automatically Mean Overload — Possible Solution ==================================================================== WHAT %util ACTUALLY MEASURES ------------------------------ Per this chapter's warn-box, "%util measures how much of the time the device had at least one request outstanding - not literally 'how full' the disk is in any simple sense." It's a measure of time-with-at- least-one-pending-request, not a measure of remaining capacity. WHY MODERN SSDs BREAK THE NAIVE READING ------------------------------ Per this chapter, "a modern SSD can handle many requests in parallel through deep internal queuing, so it's entirely possible to see %util near 100% while the device is still comfortably keeping up with additional load." An SSD with one outstanding request is already counted as 100% busy by this metric's definition, even though it may have capacity to handle many more requests simultaneously without any degradation. WHY THIS IS THE SAME CATEGORY OF MISTAKE AS CHAPTER 2's LOAD AVERAGE WARNING ------------------------------ Per this chapter, "treating %util alone as 'the disk is maxed out' is the same category of mistake as reading a high load average without checking core count in Chapter 2." Both metrics can look alarmingly high while actually representing healthy, comfortably-handled load, once you know the specific detail (core count for load average; queue depth for %util) needed to interpret them correctly. WHAT TO CHECK INSTEAD ------------------------------ Per this chapter's own busy-vs-slow table, pairing %util with await is what actually distinguishes healthy-but-busy from genuinely struggling - high %util alongside low await means busy but healthy, not overloaded. WHY THIS WORKS AS AN ANSWER ------------------------------ It explains the specific technical definition of %util, why deep queuing on modern SSDs breaks a naive "100% = maxed out" reading, and draws the chapter's own explicit parallel to the load-average mistake from Chapter 2 rather than treating this as an isolated caveat.