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Persistent Storage Using iSCSI

Overview

You can provision your OpenShift cluster with persistent storage using iSCSI. Some familiarity with Kubernetes and iSCSI 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 iSCSI is iSCSI target portal, valid iSCSI IQN, valid LUN number, and filesystem type, and the PersistentVolume API.

example 1. Persistent Volume Object Definition
apiVersion: v1
kind: PersistentVolume
metadata:
  name: iscsi-pv
spec:
  capacity:
    storage: 1Gi
  accessModes:
    - ReadWriteOnce
  iscsi:
     targetPortal: 10.16.154.81
     iqn: iqn.2014-12.example.server:storage.target00
     lun: 0
     fsType: 'ext4'
     readOnly: false

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.

iSCSI 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 iSCSI LUN must be accessible by all nodes in the cluster.