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Automatic volume expansion

Contributors joan-ing
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Automatic volume expansion enables Persistent Volumes (PVs) provisioned by Trident to grow automatically when their used capacity reaches a defined threshold.

This capability is implemented using Autogrow Policies (AGPs). An Autogrow Policy defines:

  • The utilization threshold that triggers expansion

  • The amount by which the volume grows

  • The maximum size the volume can reach

Automatic volume expansion reduces operational overhead and helps prevent application disruption caused by full volumes.

Requirements

  • Trident 26.02 or later

  • RBAC permissions to create TridentAutogrowPolicy custom resources

  • StorageClasses must include allowVolumeExpansion: true

  • Supported ONTAP protocols:

    • NFS

    • iSCSI

    • FCP

    • NVMe

Note ONTAP NVMe raw block volumes earlier than ONTAP 9.16.1 do not support automatic expansion.
Note For SAN volumes, if growthAmount is less than or equal to 50MiB, Trident increases the value to 51MiB before resizing, provided the resulting size does not exceed maxSize.
Note In brownfield environments, automatic expansion might not function for certain existing volumes due to volume publication migration behavior.

Create an Autogrow Policy

Autogrow Policies are Kubernetes custom resources of type TridentAutogrowPolicy.

An Autogrow Policy defines when and how volumes expand.

Field definitions

Field Description Required

metadata.name

Unique policy identifier.

Yes

usedThreshold

Percentage of used capacity that triggers expansion.

Yes

growthAmount

Amount to grow when the threshold is reached. Can be specified as a percentage (for example, "10%") or a fixed size (for example, "5Gi"). Defaults to 10% if not specified.

No

maxSize

Maximum volume size limit. If not specified, the volume can grow without an enforced upper limit.

No

Example: Standard Autogrow Policy

The following example creates a policy that triggers expansion at 80% utilization, grows by 10%, and limits growth to 500Gi.

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

Create the policy

  1. Save the YAML definition to a file.

  2. Apply the policy:

kubectl apply -f autogrow-policy.yaml

  1. Verify creation:

kubectl get tridentautogrowpolicy standard-autogrow

Expected output:

NAME                USED THRESHOLD   GROWTH AMOUNT   STATE
standard-autogrow   80%              10%             Success

Configuration examples

Conservative policy for production databases

Use a lower threshold and larger growth increment for production database workloads where avoiding capacity exhaustion is critical.

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

Log storage with fixed growth

Use a fixed-size increment when predictable growth steps are preferred.

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

Autogrow Policy with defaults

If only usedThreshold is specified, growthAmount defaults to 10% and maxSize is unlimited.

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

Autogrow Policy with default growthAmount

Specify a maximum size while using the default growth increment.

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

Autogrow Policy with default maxSize

Allow unrestricted growth while specifying a custom growth percentage.

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

Autogrow Policy with fractional percentages

Fractional percentages allow granular control of thresholds and growth increments.

apiVersion: trident.netapp.io/v1
kind: TridentAutogrowPolicy
metadata:
  name: fractional-policy
spec:
  usedThreshold: "80.28%"
  growthAmount: "10.65%"
  maxSize: "100Gi"

Policy states

State Description

Success

Policy validated and ready for use.

Failed

Validation errors detected. Review and correct the specification.

Deleting

Deletion in progress. Finalizers prevent removal while volumes reference the policy.

Manage Autogrow Policies

List policies

kubectl get tridentautogrowpolicy

View policy details

kubectl describe tridentautogrowpolicy production-db-policy

Using tridentctl

tridentctl get autogrowpolicy
tridentctl get autogrowpolicy production-db-policy -o yaml

Update an Autogrow Policy

Important Changes affect all volumes currently using the policy. 
kubectl edit tridentautogrowpolicy production-db-policy

Updates apply during the next growth operation. Volume restart is not required.

Delete an Autogrow Policy

Autogrow Policies include finalizer protection to prevent deletion while in use.

kubectl delete tridentautogrowpolicy production-db-policy

If volumes reference the policy, it remains in the Deleting state until all references are removed.

To identify volumes using a policy:

tridentctl get autogrowpolicy production-db-policy -o yaml

Remove policy from volumes:

kubectl annotate pvc <pvc-name> \
  trident.netapp.io/autogrowPolicy="none" \
  --overwrite

Configure Autogrow Policy on a StorageClass

Associate a policy using the trident.netapp.io/autogrowPolicy 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

Verify annotation:

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

Update Autogrow Policy on a StorageClass

kubectl annotate storageclass ontap-gold \
  trident.netapp.io/autogrowPolicy="standard-autogrow" \
  --overwrite

Remove Autogrow Policy from a StorageClass

Option 1: Remove annotation

kubectl annotate storageclass ontap-gold \
  trident.netapp.io/autogrowPolicy-

Option 2: Set annotation to none

kubectl annotate storageclass ontap-gold \
  trident.netapp.io/autogrowPolicy="none" \
  --overwrite

Apply Autogrow Policy to a PVC

Apply a policy at the PVC level to override StorageClass behavior.

apiVersion: v1
kind: PersistentVolumeClaim
metadata:
  name: database-pvc
  annotations:
    trident.netapp.io/autogrowPolicy: "production-db-policy"
spec:
  storageClassName: ontap-gold
  accessModes:
    - ReadWriteOnce
  resources:
    requests:
      storage: 500Gi

Disable Autogrow on a PVC:

kubectl annotate pvc database-pvc \
  trident.netapp.io/autogrowPolicy="none" \
  --overwrite

Monitor Autogrow Policy Usage

List policies:

kubectl get tridentautogrowpolicy

Find which policy a PVC uses:

kubectl get pvc database-pvc \
  -o jsonpath='{.metadata.annotations.trident\.netapp\.io/autogrowPolicy}'

Monitor events:

kubectl get events \
  --field-selector involvedObject.kind=TridentAutogrowPolicy

Troubleshooting

Issue Possible cause Resolution

Policy in Failed state

Invalid specification

Correct the policy and reapply

Volume does not expand

maxSize reached

Increase maxSize

Frequent expansions

Threshold too low

Increase usedThreshold

PVC shows AutogrowPolicyNotFound

Policy does not exist

Verify policy name

PVC shows AutogrowPolicyNotUsable

Policy in Failed state

Resolve validation errors

TAGRI repeatedly rejected

maxSize exceeded

Increase maxSize or adjust growthAmount