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Configure ONTAP volume autosize

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Configure Trident to enable ONTAP volume autosize on the FlexVol volumes that back persistent volumes. When used space reaches a configured threshold, ONTAP automatically grows the FlexVol up to a maximum size. This provides additional capacity for snapshots and storage overhead without manually resizing the FlexVol.

ONTAP volume autosize grows the backing FlexVol only; it does not change the PersistentVolumeClaim (PVC) size. This differs from Trident Autogrow Policies, which expand the PVC.

Trident applies backend autosize settings when it creates, clones, or resizes a volume, and when it imports a volume that it manages.

Requirements

  • Trident 26.10 or later.

  • One of the following drivers:

    • ontap-san with iSCSI, NVMe, or Fibre Channel Protocol (FCP).

    • ontap-san-economy with iSCSI.

  • On-premises ONTAP:

    • For backends using ONTAP REST APIs, ONTAP 9.12.1 or later. NVMe backends must use ONTAP REST APIs.

    • For backends using ONTAPI (ZAPI), any ONTAP version supported by Trident. See Trident requirements.

Limitations

  • ONTAP volume autosize does not shrink FlexVols.

  • Autosize is configured per backend. Create separate backends to use different settings for different workloads.

  • ONTAP volume autosize is not supported on ONTAP NAS drivers, ASA r2 systems, NetApp AFX or other disaggregated ONTAP systems, or Google Cloud NetApp Volumes. Backend creation fails for these configurations.

  • TridentMirrorRelationship replication and MetroCluster configurations are not supported with ONTAP volume autosize. Trident does not prevent these configurations.

  • For ontap-san-economy, maximumSize must be a percentage.

  • For ontap-san, an absolute maximumSize acts as a size limit. Creating or expanding a PVC fails if the backing FlexVol must exceed that limit.

  • An ontap-san-economy FlexVol can contain LUNs for multiple PVCs. Each volume operation applies the current backend's autosize settings to the whole FlexVol. If multiple backends share FlexVols, the most recent operation determines their settings. For ontap-san-economy, configure only mode: grow and omit growThresholdPercent and maximumSize so all backends use the same defaults.

ONTAP volume autosize options

Set these options in the top-level ontapAutosize block of the backend configuration.

Option Description Format Required Default when ontapAutosize is present Example

mode

Enables or disables autosize. grow enables autosize; off disables it.

String

No

off

grow or off

growThresholdPercent

Used-space percentage at which ONTAP grows the FlexVol. Valid values are from 2 through 99.

Integer

No

85

90

maximumSize

Maximum FlexVol size, expressed as a percentage of its size or as an absolute size. Absolute sizes are supported only for ontap-san.

Percentage or Kubernetes quantity

No

"20%"

"20%" or "2Ti"

The defaults apply when the ontapAutosize block is present. If you omit the block, Trident does not change the autosize settings on FlexVols.

Trident converts a percentage maximumSize to an absolute size and recalculates it whenever the volume is resized. For example, with maximumSize: "20%", a 100 GiB FlexVol can grow to 120 GiB.

Configure ONTAP volume autosize

  1. Add the ontapAutosize block to your backend configuration:

    apiVersion: trident.netapp.io/v1
kind: TridentBackendConfig
metadata:
  name: backend-tbc-ontap-san
  namespace: trident
spec:
  version: 1
  storageDriverName: ontap-san
  backendName: ontap-san-autosize
  managementLIF: 10.0.0.1
  svm: svm_san
  sanType: iscsi
  ontapAutosize:
    mode: grow
    growThresholdPercent: 85
    maximumSize: "20%"
  credentials:
    name: backend-tbc-ontap-san-secret

  2. Create the backend:

    kubectl -n trident create -f backend-tbc-ontap-san.yaml

  3. After provisioning a volume from this backend, verify the autosize settings applied to its Trident volume:

    kubectl get tridentvolume <pv-name> -n trident \
  -o jsonpath='{.config.ontapAutosizeMode} {.config.ontapAutosizeGrowThresholdPercent} {.config.ontapAutosizeMaximumSize}'

    For the configuration above, the expected output is:

    grow 85 20%

Update autosize settings on a backend

You can add, change, or remove the ontapAutosize block by updating the backend. The change does not immediately update existing FlexVols:

  • For ontap-san, new volumes, clones, and managed imports use the new settings. Existing volumes retain their current settings, including when they are resized.

  • For ontap-san-economy, the shared FlexVol receives the new settings the next time Trident creates, resizes, clones, or imports a volume in it.

Configuration examples

ontap-san with FCP and an absolute maximum size

{
  "version": 1,
  "storageDriverName": "ontap-san",
  "managementLIF": "10.0.0.1",
  "svm": "svm_san",
  "username": "vsadmin",
  "password": "<password>",
  "sanType": "fcp",
  "ontapAutosize": {
    "mode": "grow",
    "growThresholdPercent": 90,
    "maximumSize": "2Ti"
  }
}

ontap-san-economy

This example sets only mode, so Trident uses the default values for growThresholdPercent and maximumSize:

{
  "version": 1,
  "storageDriverName": "ontap-san-economy",
  "managementLIF": "10.0.0.1",
  "svm": "svm_san",
  "username": "vsadmin",
  "password": "<password>",
  "ontapAutosize": {
    "mode": "grow"
  }
}

Frequently asked questions

Can I use ONTAP volume autosize with Trident Autogrow Policies?

Yes. A Trident Autogrow Policy expands the PVC, and Trident recalculates the ONTAP autosize maximum during each resize. If you use an absolute maximumSize with ontap-san, set the policy's maxSize low enough to keep the backing FlexVol within that limit. The FlexVol is larger than the PVC because Trident adds space for snapshot reserve and metadata.

What is the difference between omitting ontapAutosize and setting mode: off?

If you omit ontapAutosize, Trident does not change the autosize settings on ONTAP FlexVols. If you set mode: off, Trident disables autosize on FlexVols it creates or updates, including clones that inherited autosize settings from their source.

Why did my PVC expansion fail with an ontapAutosize maximum …​ is below required FlexVol size error?

The volume uses an absolute maximumSize, and the expanded PVC requires a larger FlexVol. An ontap-san volume retains the maximum size it was created with, so updating the backend does not change the setting on existing volumes. For new volumes, increase maximumSize or use a percentage.

Why did volume creation fail with an autosize error?

ONTAP rejected the autosize settings, and the PVC events include the reason from ONTAP. For example, the maximum size might exceed the largest FlexVol size supported by the ONTAP system. Lower maximumSize on the backend; Trident uses the updated value the next time it attempts to create a volume.