Persistent storage using Fibre Channel

OKD supports Fibre Channel, allowing you to provision your OKD cluster with persistent storage using Fibre channel volumes. 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. Persistent volumes are not bound to a single project or namespace; they can be shared across the OKD cluster. Persistent volume claims are specific to a project or namespace and can be requested by users.

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

Additional resources

Provisioning

To provision Fibre Channel volumes using the PersistentVolume API the following must be available:

  • The targetWWNs (array of Fibre Channel target’s World Wide Names).

  • A valid LUN number.

  • The filesystem type.

A persistent volume and a LUN have a one-to-one mapping between them.

Prerequisites

  • Fibre Channel LUNs must exist in the underlying infrastructure.

PersistentVolume object definition

  1. apiVersion: v1
  2. kind: PersistentVolume
  3. metadata:
  4.   name: pv0001
  5. spec:
  6.   capacity:
  7.     storage: 1Gi
  8.   accessModes:
  9.     - ReadWriteOnce
  10.   fc:
  11.     wwids: [scsi-3600508b400105e210000900000490000] (1)
  12.     targetWWNs: ['500a0981891b8dc5', '500a0981991b8dc5'] (2)
  13.     lun: 2 (2)
  14.     fsType: ext4
1World wide identifiers (WWIDs). Either FC wwids or a combination of FC targetWWNs and lun must be set, but not both simultaneously. The FC WWID identifier is recommended over the WWNs target because it is guaranteed to be unique for every storage device, and independent of the path that is used to access the device. The WWID identifier can be obtained by issuing a SCSI Inquiry to retrieve the Device Identification Vital Product Data (page 0x83) or Unit Serial Number (page 0x80). FC WWIDs are identified as /dev/disk/by-id/ to reference the data on the disk, even if the path to the device changes and even when accessing the device from different systems.
2Fibre Channel WWNs are identified as /dev/disk/by-path/pci-<IDENTIFIER>-fc-0x<WWN>-lun-<LUN#>, but you do not need to provide any part of the path leading up to the WWN, including the 0x, and anything after, including the - (hyphen).

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 mapped to a single persistent volume, and unique names must be used for persistent volumes.

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

Fibre Channel volume security

Users request storage with a persistent volume claim. 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.