vSphere CSI Driver - Raw Block Volume

Raw Block Volume feature in Kubernetes was promoted to stable in Kubernetes 1.18. vSphere CSI Driver release v2.3.0 onwards has Raw Block Volume feature released as Alpha. We do not recommend Alpha features for production use.

This feature allows persistent volumes to be exposed inside containers as a block device instead of as a mounted file system.

There are some specialized applications that require direct access to a block device because the file system layer introduces unneeded overhead. The ability to use a raw block device without a filesystem will allow Kubernetes better support for high-performance applications that are capable of consuming and manipulating block storage for their needs. The most common case is databases (MongoDB, Cassandra) that require consistent I/O performance and low latency, which prefer to organize their data directly on the underlying storage.

Creating a new raw block PVC

To request a raw block PersistentVolumeClaim, volumeMode = "Block" must be specified in the PersistentVolumeClaimSpec.

apiVersion: v1
kind: PersistentVolumeClaim
metadata:
  name: block-pvc
spec:
  accessModes:
    - ReadWriteMany
  volumeMode: Block
  storageClassName: example-vanilla-block-sc
  resources:
    requests:
      storage: 1Gi

Using a raw block PVC

When you use the PVC in a pod definition, you get to choose the device path for the block device rather than the mount path for the file system.

apiVersion: v1
kind: Pod
metadata:
  name: block-pod
spec:
  containers:
  - name: test-container
    image: gcr.io/google_containers/busybox:1.24
    command: ["/bin/sh", "-c", "while true ; do sleep 2 ; done"]
    volumeDevices:
    - devicePath: /dev/xvda
      name: data
  restartPolicy: Never
  volumes:
  - name: data
    persistentVolumeClaim:
      claimName: block-pvc