Starting with v1.10.0, Longhorn supports online expansion for v2 data engine volumes that use the NVMe frontend. This feature allows users to expand a volume to the requested size while keeping the workload running.

During the expansion process, Longhorn automatically resizes all replicas to match the user-requested size. This eliminates the need to stop or detach the application from the volume, ensuring a seamless and non-disruptive scaling of storage.

This capability significantly improves flexibility in storage management by enabling volumes to be scaled without any downtime.

How to use

When creating the v2 volume from UI

1. Select a volume with Block Device or NVMf as the frontend.
2. Navigate to the Volumes page in the Longhorn UI.
3. Click Expand Volume from the volume operations menu.
4. Enter the new desired size and confirm. The expansion will begin automatically.

When creating the v2 volume from manifest

1. Create a StorageClass for the v2 data engine. Make sure allowVolumeExpansion is set to true. For example:

   kind: StorageClass
   apiVersion: storage.k8s.io/v1
   metadata:
       name: longhorn-v2-data-engine
   provisioner: driver.longhorn.io
   allowVolumeExpansion: true
   reclaimPolicy: Delete
   volumeBindingMode: Immediate
   parameters:
     numberOfReplicas: "3"
     staleReplicaTimeout: "2880"
     fsType: "ext4"
     dataEngine: "v2"
   

2. Create a PersistentVolumeClaim (PVC) that references this StorageClass:

   apiVersion: v1
   kind: PersistentVolumeClaim
   metadata:
     name: longhorn-volv-pvc
     namespace: default
   spec:
     accessModes:
       - ReadWriteOnce
     storageClassName: longhorn-v2-data-engine
     resources:
       requests:
         storage: 2Gi
   

3. To expand the volume, edit the PVC manifest to increase the storage request to a larger size, then apply the updated manifest.

     resources:
       requests:
         storage: 3Gi
   

Known Limitations

The UBLK frontend is not supported for online expansion as of v1.10.0. Attempting to expand a volume using the UBLK frontend will not be allowed.

Reference

For more information, see [FEATURE] v2 supports volume expansion.