{
  "slug": "reverse-mapping-ftl",
  "term": "Reverse mapping (FTL)",
  "aliases": [
    "Physical-to-logical mapping",
    "P2L mapping"
  ],
  "definition": "An FTL reverse mapping associates a physical flash location with logical addresses that refer to its contents.",
  "note": "Historical page metadata need not describe every current reference after address sharing. Collection and recovery must reconcile the changed associations, rather than trust an obsolete address stored with the page. [remap]\n\nThe logical-to-physical map serves host lookups; the reverse direction supports relocation and reconstruction. Neither mapping direction alone defines a flush or transaction guarantee. [remap] [scftl]\n\nIn SCFTL, a stored physical-to-logical pair p to l is invalid if the current logical-to-physical map no longer sends l to p. The reverse entry can remain as history without making p live. [scftl]",
  "status": "shipping",
  "advantages": [],
  "limitations": [],
  "related": [
    "ftl",
    "page-level-mapping",
    "garbage-collection",
    "snapshot-consistent-ftl"
  ],
  "supersedes": [],
  "supersededBy": [],
  "firstSeen": null,
  "lastSeen": null,
  "updated": "2026-11-08",
  "citations": [
    {
      "id": "remap",
      "title": "Zhou et al. Remap-SSD. FAST 2021, pp. 187-202, sections 2-4: reverse mappings and remapping consistency.",
      "url": "https://www.usenix.org/system/files/fast21-zhou.pdf",
      "accessed": "2026-11-08"
    },
    {
      "id": "scftl",
      "title": "Chang et al. Determinizing Crash Behavior with a Verified Snapshot-Consistent Flash Translation Layer. OSDI 2020, sections 3.2-3.4.",
      "url": "https://www.usenix.org/system/files/osdi20-chang.pdf",
      "accessed": "2026-11-08"
    },
    {
      "id": "hesela",
      "title": "Hesela: shared flash pages and reverse mappings",
      "url": "https://hesela.com/analyses/ssd-mapping-cache-hmb/#reverse-mapping",
      "accessed": "2026-11-08"
    }
  ]
}