{
  "slug": "gray-failure",
  "term": "Gray failure",
  "aliases": [
    "grey failure"
  ],
  "definition": "A gray failure occurs when an application observes a system as unhealthy while that system's failure observer regards it as healthy.",
  "note": "This observer-relative definition is broader than slow hardware: it can include intermittent errors and capacity problems. A slowdown detected by both observers need not be gray in this sense. [huang-hotos17]",
  "related": [
    "fail-slow",
    "differential-observability"
  ],
  "citations": [
    {
      "id": "huang-hotos17",
      "title": "Huang et al., Gray Failure: The Achilles' Heel of Cloud-Scale Systems, HotOS 2017, section 3; DOI 10.1145/3102980.3103005.",
      "url": "https://www.microsoft.com/en-us/research/wp-content/uploads/2017/06/paper-1.pdf",
      "accessed": "2026-10-13"
    },
    {
      "id": "hesela-observers",
      "title": "Hesela: Fail-slow NVMe SSDs: what SMART and heartbeats miss",
      "url": "https://hesela.com/analyses/nvme-fail-slow-unseen-by-smart/",
      "accessed": "2026-10-13"
    }
  ],
  "status": "unknown",
  "advantages": [],
  "limitations": [],
  "supersedes": [],
  "supersededBy": [],
  "firstSeen": null,
  "lastSeen": null,
  "updated": "2026-10-13"
}