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Persistent Storage Using Fibre Channel

Overview

You can provision your OpenShift cluster with persistent storage using Fibre Channel. Some familiarity with Kubernetes and Fibre Channel is assumed.

The Kubernetes persistent volume framework allows administrators to provision a cluster with persistent storage and gives users a way to request those resources without having any knowledge of the underlying infrastructure.

High-availability of storage in the infrastructure is left to the underlying storage provider.

Provisioning

Storage must exist in the underlying infrastructure before it can be mounted as a volume in OpenShift. All that is required for Fibre Channel persistent storage is the targetWWNs (array of Fibre Channel target’s World Wide Names), a valid LUN number, and filesystem type, and the PersistentVolume API. Note, the number of LUNs must correspond to the number of Persistent Volumes that are created. In the example below, we have LUN as 2, therefore we have created two Persistent Volume definitions.

Example 1. Persistent Volumes Object Definition
apiVersion: v1
kind: PersistentVolume
metadata:
  name: pv0001
spec:
  capacity:
    storage: 1Gi
  accessModes:
    - ReadWriteOnce
  fc:
    targetWWNs: ['500a0981891b8dc5', '500a0981991b8dc5']
    lun: 2
    fsType: ext4
apiVersion: v1
kind: PersistentVolume
metadata:
  name: pv0002
spec:
  capacity:
    storage: 1Gi
  accessModes:
    - ReadOnlyMany
  fc:
    targetWWNs: ['500a0981891b8dc5', '500a0981991b8dc5']
    lun: 2
    fsType: ext4

Changing the value of the fstype parameter after the volume has been formatted and provisioned can result in data loss and pod failure.

Enforcing Disk Quotas

Use LUN partitions to enforce disk quotas and size constraints. Each LUN is one persistent volume. Kubernetes enforces unique names for persistent volumes.

Enforcing quotas in this way allows the end user to request persistent storage by a specific amount (e.g, 10Gi) and be matched with a corresponding volume of equal or greater capacity.

Fibre Channel Volume Security

Users request storage with a PersistentVolumeClaim. This claim only lives in the user’s namespace and can only be referenced by a pod within that same namespace. Any attempt to access a persistent volume across a namespace causes the pod to fail.

Each Fibre Channel LUN must be accessible by all nodes in the cluster.