{
  "slug": "differential-raid",
  "term": "Differential RAID",
  "aliases": [
    "Diff-RAID"
  ],
  "definition": "Differential RAID is a research design that combines uneven parity placement with parity reassignment during replacement to maintain different SSD wear ages.",
  "note": "The EuroSys 2010 design targets wear-driven reliability under its model; merely using a dedicated parity drive is insufficient. Full-row writes weaken the intended write imbalance [diffraid2010].\n\nFor a worked calculation, distinguish parity share, member writes, NAND erasures and device failure risk. Host-data volume, not the fraction of requests, weights mixtures of small and full-row writes [hesela-placement].",
  "status": "research",
  "advantages": [
    "Makes the relationship between redundancy placement and per-member write load explicit"
  ],
  "limitations": [
    "Write-count differences do not establish a present-day reliability improvement",
    "Parity reassignment adds replacement work"
  ],
  "related": [
    "raid-5",
    "full-stripe-write",
    "read-modify-write",
    "wear-leveling",
    "write-amplification"
  ],
  "supersedes": [],
  "supersededBy": [],
  "firstSeen": null,
  "lastSeen": null,
  "updated": "2026-10-20",
  "citations": [
    {
      "id": "diffraid2010",
      "title": "Balakrishnan et al. Differential RAID: Rethinking RAID for SSD Reliability. EuroSys 2010, sections 3-4.",
      "url": "https://www.microsoft.com/en-us/research/wp-content/uploads/2010/04/BKPM-Eurosys2010.pdf",
      "accessed": "2026-10-20"
    },
    {
      "id": "hesela-placement",
      "title": "Hesela: parity placement and per-member writes",
      "url": "https://hesela.com/analyses/raid-write-penalty-io-not-speed/#parity-placement",
      "accessed": "2026-10-20"
    }
  ]
}