{
  "slug": "block-invalidation-time",
  "term": "Block invalidation time",
  "aliases": [
    "block death time",
    "BIT (storage placement)"
  ],
  "definition": "Block invalidation time is the point at which a stored block version becomes obsolete, rather than the duration for which it remained valid.",
  "note": "Equal lifetimes do not imply equal invalidation endpoints when versions were written at different times. [unwritten-contract]\n\nSepBIT infers placement from user-write history and surviving GC-rewritten blocks, rather than assuming perfect knowledge of future invalidations. Its logical clock advances on user writes, not GC rewrites. [sepbit]\n\nKeep the observation unit explicit: elapsed seconds, intervening workload writes and physical erase cycles are different quantities.",
  "status": "research",
  "related": [
    "hot-cold-data-separation",
    "garbage-collection",
    "greedy-garbage-collection",
    "write-amplification"
  ],
  "advantages": [],
  "limitations": [
    {
      "text": "An estimated invalidation time is not a guaranteed overwrite deadline, and a placement heuristic does not establish device-level write amplification.",
      "citationIds": [
        "sepbit"
      ]
    }
  ],
  "supersedes": [],
  "supersededBy": [],
  "firstSeen": null,
  "lastSeen": null,
  "citations": [
    {
      "id": "unwritten-contract",
      "title": "He et al. The Unwritten Contract of Solid State Drives. EuroSys 2017, section 3.4. DOI: 10.1145/3064176.3064187.",
      "url": "https://research.cs.wisc.edu/wind/Publications/eurosys17-he.pdf",
      "accessed": "2026-11-14"
    },
    {
      "id": "sepbit",
      "title": "Wang et al. Separating Data via Block Invalidation Time Inference for Write Amplification Reduction in Log-Structured Storage. FAST 2022.",
      "url": "https://www.usenix.org/system/files/fast22-wang.pdf",
      "accessed": "2026-11-14"
    },
    {
      "id": "hesela-op",
      "title": "Hesela: SSD over-provisioning and conditional overwrite probabilities",
      "url": "https://hesela.com/analyses/ssd-overprovisioning-denominators/",
      "accessed": "2026-11-14"
    }
  ],
  "updated": "2026-11-14",
  "provenance": [
    "Primary-source synthesis; related age-conditioning arithmetic is explicitly hypothetical, not a hardware experiment or reproduction of the SepBIT prototype."
  ]
}