{
  "slug": "slowdown-ratio",
  "term": "Slowdown ratio",
  "aliases": [
    "Perseus slowdown ratio"
  ],
  "definition": "In Perseus, the slowdown ratio is observed drive latency divided by the workload-dependent upper prediction bound for that latency.",
  "note": "Use the same units for numerator and denominator: a ratio above one exceeds the bound. Section 4.4 and its example establish this direction despite the reversed Figure 9 caption. This is a sample-level quantity, not a calibrated failure probability or a drive diagnosis. [perseus]",
  "related": [
    "fail-slow",
    "latency-storage"
  ],
  "citations": [
    {
      "id": "perseus",
      "title": "Lu et al. Perseus: A Fail-Slow Detection Framework for Cloud Storage Systems. FAST 2023, sections 4.4-4.5, pp. 55-56.",
      "url": "https://www.usenix.org/system/files/fast23-lu.pdf",
      "accessed": "2026-10-14"
    },
    {
      "id": "hesela-examples",
      "title": "Hesela: synthetic slowdown-ratio arithmetic, source and tests",
      "url": "https://hesela.dev/data/slowdown-ratio-examples.json",
      "accessed": "2026-10-14"
    }
  ],
  "status": "research",
  "advantages": [],
  "limitations": [],
  "supersedes": [],
  "supersededBy": [],
  "firstSeen": null,
  "lastSeen": null,
  "updated": "2026-10-14"
}