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Milvus Volume Expansion

This guide will give an overview on how the KubeDB Ops-manager operator expands the persistent volumes of a Milvus database.

Before You Begin

• You should be familiar with the following KubeDB concepts:
  • Milvus
  • MilvusOpsRequest

How Volume Expansion Process Works

Volume expansion grows the persistent volumes backing Milvus. A MilvusOpsRequest of type VolumeExpansion carries the new size and an expansion mode:

spec:
  type: VolumeExpansion
  volumeExpansion:
    mode: Online            # Online or Offline
    node: 4Gi               # standalone target
    # streamingnode: 4Gi    # distributed target

Which key you set depends on the topology, because only certain workloads carry persistent storage:

• Standalone: use node — the standalone workload’s spec.storage.
• Distributed: use streamingnode — among the distributed roles, only streamingnode carries a persistent volume (spec.topology.distributed.streamingnode.storage). The other roles (mixcoord, datanode, querynode, proxy) are stateless and are not the focus of volume operations.

mode selects how the expansion is performed:

• Online — the volume is expanded without taking the pod down (where the storage class/CSI driver supports online resize).
• Offline — the pod is taken down, the volume is resized, and the pod is brought back up.

Storage class requirement: the underlying StorageClass must have allowVolumeExpansion: true. The base examples use local-path, which does not support expansion. Use an expansion-capable class (for example longhorn-custom) for volume expansion.

The flow is:

1. A user creates a MilvusOpsRequest of type VolumeExpansion.
2. The operator validates the request and pauses the Milvus database.
3. The operator patches the PVCs to the new size and waits for the CSI driver to complete the resize.
4. The new size is reflected in spec.storage (standalone) or spec.topology.distributed.streamingnode.storage (distributed).
5. The operator resumes the database and marks the MilvusOpsRequest as Successful.

In the next doc, we will see a step-by-step guide on expanding the volume of a Milvus database.