Persistent storage using GCE Persistent Disk

OKD supports GCE Persistent Disk volumes (gcePD). You can provision your OKD cluster with persistent storage using GCE. Some familiarity with Kubernetes and GCE 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.

GCE Persistent 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) plugin to provision gcePD 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 plugins 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 GCE 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.

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

    2. Enter a unique name for the storage claim.

    3. Select the access mode. This selection determines the read and write access for the 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 the volume 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 verification enables you to use unformatted GCE volumes as persistent volumes, because OKD formats them before the first use.