{
  "slug": "d-graid",
  "term": "D-GRAID",
  "aliases": [
    "Degrades Gracefully RAID"
  ],
  "definition": "D-GRAID is a research storage-array design that combines fault-isolated placement and selective metadata replication to preserve access to surviving files after excess failures.",
  "note": "The FAST 2004 Alexander prototype supported ext2 and VFAT with RAID-0 or RAID-1 user-data layouts; RAID-5 support was future work. Replicated naming metadata keeps surviving files reachable, while additional striped copies recover parallelism lost by fault-isolated placement. [dgraid04]\n\nIts live-block recovery conservatively includes possibly live blocks because delayed filesystem updates can make on-disk allocation information stale. This is a filesystem-aware prototype, not OpenZFS dRAID or a generic degraded-array state. [dgraid04] [zconcepts23]",
  "status": "research",
  "limitations": [
    {
      "text": "Partial availability depends on surviving metadata and file placement; it does not guarantee that every file survives.",
      "citationIds": [
        "dgraid04"
      ]
    }
  ],
  "related": [
    "degraded-array",
    "raid-rebuild",
    "draid",
    "distributed-spare"
  ],
  "citations": [
    {
      "id": "dgraid04",
      "title": "Sivathanu, Prabhakaran, A. C. Arpaci-Dusseau and R. H. Arpaci-Dusseau. Improving Storage System Availability with D-GRAID. FAST 2004, sections 3, 5-7 and 9.",
      "url": "https://www.usenix.org/legacy/events/fast04/tech/sivathanu/sivathanu.pdf",
      "accessed": "2026-11-09"
    },
    {
      "id": "zconcepts23",
      "title": "OpenZFS 2.3 zpoolconcepts(7): dRAID virtual devices and hot spares.",
      "url": "https://openzfs.github.io/openzfs-docs/man/v2.3/7/zpoolconcepts.7.html",
      "accessed": "2026-11-09"
    },
    {
      "id": "hesela-rebuild",
      "title": "Hesela: partial file availability, dRAID and recovery milestones",
      "url": "https://hesela.com/analyses/raid-rebuild-ure-math-and-resilver/#dgraid-availability",
      "accessed": "2026-11-09"
    }
  ],
  "advantages": [],
  "supersedes": [],
  "supersededBy": [],
  "firstSeen": null,
  "lastSeen": null,
  "updated": "2026-11-09"
}