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Persistent Storage Using Fibre Channel

Overview

You can provision your OKD cluster with persistent storage using Fibre Channel (FC). Some familiarity with Kubernetes and FC 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 OKD. All that is required for FC persistent storage is the PersistentVolume API, the wwids or the targetWWNs with a valid lun number, and the fsType. Persistent volume and a LUN have one-to-one mapping between them.

Persistent Volume Object Definition
apiVersion: v1
kind: PersistentVolume
metadata:
  name: pv0001
spec:
  capacity:
    storage: 1Gi
  accessModes:
    - ReadWriteOnce
  fc:
    wwids: [scsi-3600508b400105e210000900000490000] (1)
    targetWWNs: ['500a0981891b8dc5', '500a0981991b8dc5'] (2)
    lun: 2 (2)
    fsType: ext4
1 Optional: World 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.
2 Optional: World wide names (WWNs). 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. FC 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 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, such as 10 Gi, 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 namespace of the user and can only be referenced by a pod within that same namespace. Any attempt to access a persistent volume claim across a namespace causes the pod to fail.

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