{
  "slug": "raidz-expansion",
  "term": "RAIDZ expansion",
  "aliases": [
    "RAID-Z expansion"
  ],
  "definition": "RAIDZ expansion widens an existing RAIDZ virtual device by attaching another member and redistributing allocated space while retaining old blocks' data-to-parity ratios.",
  "note": "OpenZFS 2.3 documents unchanged parity level and different ratios for pre-expansion and newly allocated blocks. [attach] This is capacity expansion, not replacement-device resilvering. The implementation records logical widths over transaction-group history to interpret blocks after reflow. [geometry] See the companion analysis for a bounded accounting model, not a pool-capacity estimator.",
  "status": "shipping",
  "advantages": [],
  "limitations": [
    {
      "text": "The active raidz_expansion feature is not read-only compatible; recovery/import software must support it.",
      "citationIds": [
        "features"
      ]
    }
  ],
  "related": [
    "raidz",
    "resilver",
    "snapshot",
    "data-scrubbing"
  ],
  "supersedes": [],
  "supersededBy": [],
  "firstSeen": null,
  "lastSeen": null,
  "updated": "2026-10-16",
  "citations": [
    {
      "id": "attach",
      "title": "OpenZFS 2.3: zpool-attach(8), RAID-Z expansion and space reporting",
      "url": "https://openzfs.github.io/openzfs-docs/man/v2.3/8/zpool-attach.8.html",
      "accessed": "2026-10-16"
    },
    {
      "id": "geometry",
      "title": "OpenZFS zfs-2.3.0: vdev_raidz.c, reflow and time-dependent geometry",
      "url": "https://github.com/openzfs/zfs/blob/zfs-2.3.0/module/zfs/vdev_raidz.c",
      "accessed": "2026-10-16"
    },
    {
      "id": "features",
      "title": "OpenZFS 2.3: zpool-features(7), raidz_expansion compatibility",
      "url": "https://openzfs.github.io/openzfs-docs/man/v2.3/7/zpool-features.7.html",
      "accessed": "2026-10-16"
    },
    {
      "id": "hesela",
      "title": "Hesela: RAIDZ expansion and retained parity cost",
      "url": "https://hesela.com/analyses/raidz-expansion-parity-capacity/",
      "accessed": "2026-10-16"
    }
  ]
}