{
  "slug": "thick-provisioning",
  "term": "Thick provisioning",
  "aliases": [],
  "definition": "Thick provisioning allocates or reserves a storage object's specified capacity upfront at the providing layer instead of adding backing space only as writes arrive.",
  "note": "Thick and thin describe allocation policy, not the storage medium. SNIA contrasts allocating physical capacity as applications write with preallocating it during provisioning. Name the volume, filesystem or virtual-disk layer whose capacity is being reserved. [snia-thin]\n\nZero initialization is separate from allocation. For VMDKs on VMFS, allocation means marking filesystem space in use. A lazy-zeroed thick disk allocates that space at creation and zeroes a new block on first write; an eager-zeroed thick disk also zeroes the blocks at creation. These are VMFS policies, not universal names for array behavior. [vmfs-provisioning]\n\nA thick virtual disk can still use thin backing. A May 2021 array integration guide documents lazy-zeroed and eager-zeroed thick VMDKs remaining thin at the array layer. In the described firmware configurations, sequential zeros are tracked without writing the zero-filled pages to drives. This is configuration-specific, not a guarantee for every array. [sc-series-provisioning]\n\nThe cited volume provisioning policy reserves aggregate capacity for a thick volume. The documented overwrite assurance for a file or LUN also requires space reservation on that object. Volume provisioning and object reservation must therefore be checked together; a generic thick label is not enough. [ontap-volumes]",
  "status": "shipping",
  "advantages": [],
  "limitations": [
    {
      "text": "An upper-layer allocation does not establish that lower thin-provisioned storage has reserved the same capacity.",
      "citationIds": [
        "vmfs-provisioning",
        "sc-series-provisioning"
      ]
    },
    {
      "text": "Upfront allocation and upfront zero initialization are different properties.",
      "citationIds": [
        "vmfs-provisioning"
      ]
    }
  ],
  "related": [
    "thin-provisioning",
    "storage-array",
    "file-preallocation",
    "logical-volume",
    "block-storage"
  ],
  "supersedes": [],
  "supersededBy": [],
  "firstSeen": null,
  "lastSeen": null,
  "citations": [
    {
      "id": "snia-thin",
      "title": "SNIA Dictionary: thin provisioning, allocation on writes versus preallocation.",
      "url": "https://www.snia.org/education/online-dictionary/term/thin-provisioning",
      "accessed": "2026-10-31"
    },
    {
      "id": "vmfs-provisioning",
      "title": "Broadcom KB 343258: Understanding large-scale sequential write performance in VMDKs residing on VMFS datastores; allocation and zeroing table.",
      "url": "https://knowledge.broadcom.com/external/article/343258",
      "accessed": "2026-10-31"
    },
    {
      "id": "sc-series-provisioning",
      "title": "Dell EMC SC Series: Best Practices with VMware vSphere, May 2021, 2060-M-BP-V, page 52, sections 12.2-12.3.",
      "url": "https://dl.dell.com/manuals/common/sc-series-vmware-vsphere-best-practices_en-us.pdf",
      "accessed": "2026-10-31"
    },
    {
      "id": "ontap-volumes",
      "title": "NetApp ONTAP 9: Learn about SAN volume provisioning, thick volumes and space-reserved file/LUN requirements.",
      "url": "https://docs.netapp.com/us-en/ontap/volumes/san-volumes-concept.html",
      "accessed": "2026-10-31"
    }
  ],
  "updated": "2026-10-31",
  "provenance": [
    "Definition synthesized from SNIA's allocation contrast and the named-layer vendor examples; not a universal configuration or a performance rating. [snia-thin] [vmfs-provisioning] [ontap-volumes]",
    "Vendor documentation review, not a benchmark or an end-to-end capacity test. The Dell SC Series example is dated May 2021 and applies to the described SCOS thin-write configurations. [sc-series-provisioning]",
    "Zero initialization here is a virtual-disk preparation operation, not a media-sanitization claim. [vmfs-provisioning]",
    "The volume and object reservation example describes ONTAP FlexVol, not all implementations. [ontap-volumes]"
  ]
}