Persistent storage using Azure

OKD supports Microsoft Azure Disk volumes. You can provision your OKD cluster with persistent storage using Azure. Some familiarity with Kubernetes and Azure 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. Azure Disk volumes can be provisioned dynamically. 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.

OKD defaults to using an in-tree (non-CSI) plug-in to provision Azure Disk storage.

In future OKD versions, volumes provisioned using existing in-tree plug-ins are planned for migration to their equivalent CSI driver. CSI automatic migration should be seamless. Migration does not change how you use all existing API objects, such as persistent volumes, persistent volume claims, and storage classes. For more information about migration, see CSI automatic migration.

After full migration, in-tree plug-ins will eventually be removed in future versions of OKD.

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

Additional resources

Creating the Azure storage class

Storage classes are used to differentiate and delineate storage levels and usages. By defining a storage class, users can obtain dynamically provisioned persistent volumes.

Procedure

  1. In the OKD console, click Storage → Storage Classes.

  2. In the storage class overview, click Create Storage Class.

  3. Define the desired options on the page that appears.

    1. Enter a name to reference the storage class.

    2. Enter an optional description.

    3. Select the reclaim policy.

    4. Select kubernetes.io/azure-disk from the drop down list.

      1. Enter the storage account type. This corresponds to your Azure storage account SKU tier. Valid options are Premium_LRS, Standard_LRS, StandardSSD_LRS, and UltraSSD_LRS.

      2. Enter the kind of account. Valid options are shared, dedicated, and managed.

        Red Hat only supports the use of kind: Managed in the storage class.

        With Shared and Dedicated, Azure creates unmanaged disks, while OKD creates a managed disk for machine OS (root) disks. But because Azure Disk does not allow the use of both managed and unmanaged disks on a node, unmanaged disks created with Shared or Dedicated cannot be attached to OKD nodes.

    5. Enter additional parameters for the storage class as desired.

  4. Click Create to create the storage class.

Additional resources

Creating the persistent volume claim

Prerequisites

Storage must exist in the underlying infrastructure before it can be mounted as a volume in OKD.

Procedure

  1. In the OKD console, click Storage → Persistent Volume Claims.

  2. In the persistent volume claims overview, click Create Persistent Volume Claim.

  3. Define the desired options on the page that appears.

    1. Select the storage class created previously from the drop-down menu.

    2. Enter a unique name for the storage claim.

    3. Select the access mode. This determines the read and write access for the created storage claim.

    4. Define the size of the storage claim.

  4. Click Create to create the persistent volume claim and generate a persistent volume.

Volume format

Before OKD mounts the volume and passes it to a container, it checks that it contains a file system as specified by the fsType parameter in the persistent volume definition. If the device is not formatted with the file system, all data from the device is erased and the device is automatically formatted with the given file system.

This allows using unformatted Azure volumes as persistent volumes, because OKD formats them before the first use.