Diagnose four slow workloads from their metrics alone

applied · 50 min · Objective 1.2

Task

Apply the whole contention objective: given four sets of symptoms, name the mechanism and the remedy for each. Three describe contention you do not own; one describes a limit you bought.

Steps

  1. Write the four cases into lab/cases.md, one paragraph each: (a) guest CPU 30%, steal time 25%, latency doubled; (b) guest memory looks fine, host shows heavy swapping, disk latency enormous; (c) a volume benchmarks at 3000 IOPS for 40 minutes then settles permanently at 120; (d) a guest with 16 vCPUs performs worse than the same workload on a guest with 4.
  2. For each, write the mechanism in lab/diagnosis.csv with columns case,mechanism,evidence,remedy,prevention.
  3. For case (c), state the specific storage feature responsible and the volume type that removes it.
  4. For case (d), explain why more vCPUs made it slower, in terms of what the hypervisor scheduler must find free simultaneously.
  5. Add a row for a fifth case of your own, taken from a real system you have seen behave badly, with the evidence you actually had.

Verify

awk -F, 'NR>1 && NF>=5 {n++} END {print n" case(s) fully diagnosed"}' lab/diagnosis.csv
grep -Eci 'burst credit' lab/diagnosis.csv
grep -Eci 'host swap|hypervisor swap' lab/diagnosis.csv
grep -Eci 'provisioned' lab/diagnosis.csv

Five cases, and each of the three named mechanisms must appear. Missing "burst credit" means case (c) was diagnosed as a generic storage problem. Case (b) is host swapping, not ballooning: a balloon inflates INSIDE the guest, so the guest would see its own memory shrink, and here it looks fine -- the hypervisor is paging the guest out behind its back. Ballooning belongs in the evidence as the stage that came first, or never came because the guest tools were missing. Case (c)'s remedy is a provisioned-performance volume, however your provider names it.

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