{
  "slug": "nand-copyback",
  "term": "NAND copyback",
  "aliases": [
    "copy-back",
    "internal data move",
    "IDM"
  ],
  "definition": "NAND copyback relocates page data through an on-chip buffer to a destination page without transferring the payload to an external controller.",
  "note": "The studied implementations constrain source and destination placement; a host copy command does not establish that NAND copyback occurred. Bypassing controller ECC can preserve read errors in the new copy, so the correction path must be specified.",
  "status": "shipping",
  "advantages": [
    {
      "text": "Can avoid the off-chip payload transfers used by a controller-mediated relocation.",
      "citationIds": [
        "hu2011"
      ]
    }
  ],
  "limitations": [
    {
      "text": "Placement restrictions are device-specific; historical odd/even rules must not be applied to every NAND generation.",
      "citationIds": [
        "hu2011"
      ]
    },
    {
      "text": "Restricted-copyback research uses conditional consecutive-copy budgets, not a universal safe count.",
      "citationIds": [
        "hong2018"
      ]
    }
  ],
  "related": [
    "nand-flash",
    "garbage-collection",
    "write-amplification",
    "ftl",
    "ldpc",
    "data-retention"
  ],
  "supersedes": [],
  "supersededBy": [],
  "firstSeen": null,
  "lastSeen": null,
  "updated": "2026-10-11",
  "citations": [
    {
      "id": "hong2018",
      "title": "Hong, Kim, Park, Jung and Kim. Revitalizing Copybacks in Modern SSDs: Why and How. Author manuscript arXiv:1810.04603v1, 2018, sections 3-5.",
      "url": "https://arxiv.org/abs/1810.04603v1",
      "accessed": "2026-10-11"
    },
    {
      "id": "hu2011",
      "title": "Hu, Jiang, Feng, Tian, Luo and Zhang. Performance Impact and Interplay of SSD Parallelism through Advanced Commands, Allocation Strategy and Data Granularity. ICS 2011, sections 2.2 and 4.3.",
      "url": "https://ranger.uta.edu/~jiang/publication/Conferences/2011/2011-ICS-Performance%20Impact%20and%20Interplay%20of%20SSD%20Parallelism%20through%20Advanced%20Commands,%20Allocation%20Strategy%20and%20Data%20Granularity.pdf",
      "accessed": "2026-10-11"
    },
    {
      "id": "han2021",
      "title": "Han, Gwak, Shin and Hwang. ZNS+: Advanced Zoned Namespace Interface for Supporting In-Storage Zone Compaction. OSDI 2021, sections 2.1 and 3.3.1.",
      "url": "https://www.usenix.org/system/files/osdi21-han.pdf",
      "accessed": "2026-10-11"
    },
    {
      "id": "hesela-copyback",
      "title": "Hesela: NAND copyback, faster relocation is not fewer writes",
      "url": "https://hesela.com/analyses/nand-copyback-ecc-boundary/",
      "accessed": "2026-10-11"
    },
    {
      "id": "example",
      "title": "Hesela illustrative copyback payload accounting: assumptions, results and model hash",
      "url": "https://hesela.dev/research/copyback-accounting.json",
      "accessed": "2026-10-11"
    }
  ]
}