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Automatic volume expansion

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Automatic volume expansion enables Persistent Volumes provisioned by Trident to grow automatically when used capacity reaches a defined threshold. This capability reduces operational overhead and helps prevent application disruption caused by capacity exhaustion.

Automatic volume expansion is implemented using Autogrow Policies. An Autogrow Policy defines:

  • The utilization threshold that triggers expansion

  • The amount by which the volume grows

  • The maximum size the volume can reach

Volumes increase in size automatically when the defined utilization threshold is exceeded. Volumes are never automatically reduced.

Requirements

Before configuring automatic volume expansion, ensure that the following requirements are met:

  • Trident 26.02 or later

  • Role-based access control permissions to create TridentAutogrowPolicy custom resources

  • StorageClasses configured with allowVolumeExpansion: true

  • Supported ONTAP protocols:

    • Network File System

    • Internet Small Computer Systems Interface

    • Fibre Channel Protocol

    • Non-Volatile Memory Express over Fabrics

Limitations

  • ONTAP Non-Volatile Memory Express raw block volumes earlier than ONTAP 9.16.1 do not support automatic expansion.

  • For storage area network volumes, if growthAmount is less than or equal to 50 mebibytes, Trident automatically increases the value to 51 mebibytes before resizing, provided the resulting size does not exceed maxSize.

  • In brownfield environments, automatic expansion might not function for certain existing volumes due to volume publication migration behavior.

  • When a volume reaches maxSize, no further expansion occurs.

  • Supported protocols for automatic volume expansion:

    • Network File System

    • Internet Small Computer Systems Interface

    • Fibre Channel Protocol

    • Non-Volatile Memory Express over Fabrics

Provision Volumes with Autogrow Policy

Autogrow Policy can be configured at two levels:

  • Storage class level: Sets default for all volumes (using annotation)

  • PVC level: Overrides storage class default (using annotation)

Create an Autogrow Policy

Autogrow Policies enable automatic volume expansion when volumes reach a defined capacity threshold.

Ensure you have:

  • Trident 26.02 or later installed

  • Role-based access control permissions to create TridentAutogrowPolicy resources

  • Understanding of workload growth requirements

An Autogrow Policy defines how volumes expand automatically when they reach a defined capacity threshold.

You can create Autogrow Policies at any point in your workflow:

  • Before StorageClasses and volumes are created

  • After StorageClasses exist

  • After volumes are provisioned

This flexibility allows you to introduce automatic expansion without recreating existing resources.

Autogrow Policy specifications

Autogrow Policies are Kubernetes custom resources defined as follows:

Field Description Format Required Example Default

name

Unique policy identifier

String

Yes

production-db-policy

None

usedThreshold

Capacity percentage that triggers expansion

Percentage string

Yes

"80%"

None

growthAmount

Amount to grow when threshold is reached

Percentage or size

No

"10%" or "5Gi"

"10%"

maxSize

Maximum volume size limit

Kubernetes quantity

No

"500Gi"

Unlimited

Create an Autogrow Policy

Steps

  1. Create a YAML file that defines your Autogrow Policy:

    apiVersion: trident.netapp.io/v1
kind: TridentAutogrowPolicy
metadata:
  name: standard-autogrow
spec:
  usedThreshold: "80%"
  growthAmount: "10%"
  maxSize: "500Gi"

  2. Apply the policy to your cluster:

    kubectl apply -f autogrow-policy.yaml

  3. Verify that the policy was created:

    kubectl get tridentautogrowpolicy standard-autogrow
    Expected output
    NAME                USED THRESHOLD   GROWTH AMOUNT   STATE
standard-autogrow   80%              10%             Success

Policy states

After you create a policy, Trident validates the specification and assigns one of the following states:

State Description Action required

Success

Policy is validated and ready to use.

None.

Failed

Validation errors detected.

Review and fix the specification.

Deleting

Deletion is in progress.

Wait for completion.

Associate a policy with a StorageClass

You can associate an Autogrow Policy with a StorageClass by using the trident.netapp.io/autogrowPolicy annotation. All volumes provisioned from that StorageClass inherit the policy.

Note The StorageClass must have allowVolumeExpansion: true.
Steps

  1. Create or modify a StorageClass with the Autogrow Policy annotation:

    apiVersion: storage.k8s.io/v1
kind: StorageClass
metadata:
  name: ontap-gold
  annotations:
    trident.netapp.io/autogrowPolicy: "production-db-policy"
provisioner: csi.trident.netapp.io
parameters:
  backendType: "ontap-san"
  fsType: "ext4"
allowVolumeExpansion: true

  2. Apply the StorageClass:

    kubectl apply -f storageclass.yaml

  3. Verify the annotation:

    kubectl get storageclass ontap-gold -o jsonpath='{.metadata.annotations.trident\.netapp\.io/autogrowPolicy}'
    Expected output
    production-db-policy

Policy precedence

When Autogrow Policy annotations are set on both a StorageClass and a PVC, Trident applies the following precedence rules:

  1. PVC annotation takes priority. If a PVC sets trident.netapp.io/autogrowPolicy, that value is always used.

  2. StorageClass annotation applies only when the PVC has no annotation.

  3. If neither has the annotation, no Autogrow Policy is applied.

Table 1. Precedence examples
StorageClass annotation PVC annotation Effective behavior

trident.netapp.io/autogrowPolicy: standard-agp

Not set

Uses standard-agp.

trident.netapp.io/autogrowPolicy: standard-agp

trident.netapp.io/autogrowPolicy: logs-policy

Uses logs-policy (PVC overrides StorageClass).

trident.netapp.io/autogrowPolicy: standard-agp

trident.netapp.io/autogrowPolicy: "none"

No Autogrow Policy (PVC disables autogrow).

Not set

trident.netapp.io/autogrowPolicy: dev-policy

Uses dev-policy.

Not set

Not set

No Autogrow Policy.

Configuration examples

The following examples show common Autogrow Policy configurations for different use cases.

Conservative policy for production databases

apiVersion: trident.netapp.io/v1
kind: TridentAutogrowPolicy
metadata:
  name: production-db-policy
spec:
  usedThreshold: "75%"
  growthAmount: "20%"
  maxSize: "5Ti"

Log storage with fixed growth increments

apiVersion: trident.netapp.io/v1
kind: TridentAutogrowPolicy
metadata:
  name: log-storage-policy
spec:
  usedThreshold: "90%"
  growthAmount: "10Gi"
  maxSize: "100Gi"

Minimal policy with defaults

When you omit growthAmount and maxSize, Trident uses the defaults (10% growth, unlimited size):

apiVersion: trident.netapp.io/v1
kind: TridentAutogrowPolicy
metadata:
  name: logs-policy
spec:
  usedThreshold: "85%"

Policy with a custom maxSize and default growthAmount

apiVersion: trident.netapp.io/v1
kind: TridentAutogrowPolicy
metadata:
  name: default-ga-policy
spec:
  usedThreshold: "70%"
  maxSize: "100Gi"

Aggressive growth with unlimited maxSize

apiVersion: trident.netapp.io/v1
kind: TridentAutogrowPolicy
metadata:
  name: aggressive-growth-policy
spec:
  usedThreshold: "80%"
  growthAmount: "150%"

Policy with fractional percentages

apiVersion: trident.netapp.io/v1
kind: TridentAutogrowPolicy
metadata:
  name: precise-policy
spec:
  usedThreshold: "80.28%"
  growthAmount: "10.65%"
  maxSize: "100Gi"
Note Fractional percentages are supported. If you specify more than three decimal places, Trident rounds the value to three decimal places.

NAS StorageClass with Autogrow

apiVersion: storage.k8s.io/v1
kind: StorageClass
metadata:
  name: ontap-nas-autogrow
  annotations:
    trident.netapp.io/autogrowPolicy: "standard-autogrow"
provisioner: csi.trident.netapp.io
parameters:
  backendType: "ontap-nas"
  fsType: "ext4"
allowVolumeExpansion: true

SAN StorageClass with Autogrow

apiVersion: storage.k8s.io/v1
kind: StorageClass
metadata:
  name: database-storage
  annotations:
    trident.netapp.io/autogrowPolicy: "production-db-policy"
provisioner: csi.trident.netapp.io
parameters:
  backendType: "ontap-san"
  fsType: "ext4"
allowVolumeExpansion: true