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Chapter 9. Dynamic provisioning

In dynamic provisioning, instead of a manually creating a pool of persistent volumes (PVs), an administrator creates a storage class. Using the storage class, OpenShift Container Platform automatically triggers the storage backend to create a brand-new volume of the exact size and type requested, creates the PV object, and then the PV binds to the persistent volume claim (PVC).

9.1. About dynamic provisioning
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The StorageClass resource object describes and classifies storage that can be requested, and provides a means for passing parameters for dynamically provisioned storage on-demand.

StorageClass objects can also serve as a management mechanism for controlling different levels of storage and access to the storage. Cluster Administrators (cluster-admin) or Storage Administrators (storage-admin) define and create the StorageClass objects that users can request without needing any detailed knowledge about the underlying storage volume sources.

The OpenShift Container Platform persistent volume framework enables this functionality and allows administrators to provision a cluster with persistent storage. The framework also gives users a way to request those resources without having any knowledge of the underlying infrastructure.

Many storage types are available for use as persistent volumes in OpenShift Container Platform. While all of them can be statically provisioned by an administrator, some types of storage are created dynamically using the built-in provider and plugin APIs.

9.2. Available dynamic provisioning plugins
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Provisioner plugins automatically create storage resources on-demand by connecting to your cloud provider’s API. This lets you dynamically provision persistent volumes (PVs) without manual intervention, adapting to your cluster’s storage needs as they arise.

Important

Any chosen provisioner plugin also requires configuration for the relevant cloud, host, or third-party provider as in the relevant documentation.

Expand
Storage typeProvisioner plugin nameNotes

Red Hat OpenStack Platform (RHOSP) Cinder

kubernetes.io/cinder

 

RHOSP Manila Container Storage Interface (CSI)

manila.csi.openstack.org

After being installed, the OpenStack Manila CSI Driver Operator and ManilaDriver automatically create the required storage classes for all available Manila share types needed for dynamic provisioning.

Amazon Elastic Block Store (Amazon EBS)

ebs.csi.aws.com

For dynamic provisioning when using multiple clusters in different zones, tag each node with Key=kubernetes.io/cluster/<cluster_name>,Value=<cluster_id> where <cluster_name> and <cluster_id> are unique per cluster.

Azure Disk

kubernetes.io/azure-disk

 

Azure File

kubernetes.io/azure-file

The persistent-volume-binder service account requires permissions to create and get secrets to store the Azure storage account and keys.

GCE Persistent Disk (gcePD)

kubernetes.io/gce-pd

In multi-zone configurations, it is advisable to run one OpenShift Container Platform cluster per GCE project to avoid persistent volumes (PVs) from being created in zones where no node exists in the current cluster.

IBM Power® Virtual Server Block

powervs.csi.ibm.com

After installation, the IBM Power® Virtual Server Block CSI Driver Operator and IBM Power® Virtual Server Block CSI Driver automatically create the required storage classes for dynamic provisioning.

VMware vSphere

kubernetes.io/vsphere-volume

 

9.3. Defining a storage class
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StorageClass objects apply cluster-wide and are available to all namespaces. Only users with cluster-admin or storage-admin privileges can create or modify them. This centralized control ensures consistent storage policies across your cluster while requiring application teams to coordinate with administrators for custom storage configurations.

Important

The Cluster Storage Operator might install a default storage class depending on the platform in use. This storage class is owned and controlled by the Operator. It cannot be deleted or modified beyond defining annotations and labels. If different behavior is required, you must define a custom storage class.

The following sections describe the basic definition for a StorageClass object and specific examples for each of the supported plugin types.

9.3.1. Basic StorageClass object definition
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A StorageClass object defines the metadata, provisioner type, and plugin-specific parameters that determine how persistent volumes (PVs) are dynamically created in your cluster. Each storage provisioner type requires different parameters, and annotations control cluster-wide defaults, making this structure the foundation for all dynamic storage provisioning.

Example StorageClass definition

kind: StorageClass
apiVersion: storage.k8s.io/v1
metadata:
  name: <storage-class-name>
  annotations:
    storageclass.kubernetes.io/is-default-class: 'true'
    ...
provisioner: kubernetes.io/aws-ebs
parameters:
  type: gp3
...

  • kind: API object type.
  • apiversion: The current apiVersion.
  • metadata.name: The name of the storage class.
  • Optional: metadata.annotations: Annotations for the storage class.
  • provisioner: The type of provisioner associated with this storage class.
  • Optional: parameters: The parameters required for the specific provisioner. This is different for each plugin.

9.3.2. RHOSP Cinder StorageObject object definition
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This RHOSP Cinder storage class example demonstrates how to configure volume types for performance optimization, control availability zone placement for high availability, and specify filesystem types for your persistent volumes.

Example Cinder storage class YAML file

kind: StorageClass
apiVersion: storage.k8s.io/v1
metadata:
  name: <storage-class-name>
provisioner: kubernetes.io/cinder
parameters:
  type: fast
  availability: nova
  fsType: ext4

  • metadata.name: Name of the storage class. The persistent volume claim uses this storage class for provisioning the associated persistent volumes.
  • parameter.type: Volume type created in Cinder. Default is empty.
  • parameters.availability: Availability Zone. If not specified, volumes are generally round-robined across all active zones where theOpenShift Container Platform cluster has a node.
  • parameters.fsType: File system that is created on dynamically provisioned volumes. This value is copied to the fsType field of dynamically provisioned persistent volumes, and the file system is created when the volume is mounted for the first time. The default value is ext4. The following is a RHOSP Cinder example storage class object definition.

9.3.3. RHOSP Manila Container Storage Interface (CSI) object definition
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The OpenStack Manila CSI Driver Operator automatically creates storage classes for all available Manila share types immediately after installation, eliminating manual configuration. This automation ensures you can start provisioning persistent volumes right away without needing to understand Manila share type details or write custom StorageClass definitions.

9.3.4. AWS Elastic Block Store (EBS) StorageObject object definition
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This AWS EBS storage class example shows how to configure volume type, IOPS performance, encryption settings, and filesystem type for dynamically provisioned persistent volumes.

Example AWS EBS storage class YAML file

kind: StorageClass
apiVersion: storage.k8s.io/v1
metadata:
  name: <storage-class-name>
provisioner: ebs.csi.aws.com
parameters:
  type: io1
  iopsPerGB: "10"
  encrypted: "true"
  kmsKeyId: keyvalue
  fsType: ext4

  • metadata.name: Name of the storage class. The persistent volume claim uses this storage class for provisioning the associated persistent volumes.
  • parameters.type: Select from io1, gp3, sc1, st1. The default is gp3. For valid Amazon Resource Name (ARN) values, see the AWS documentation, Identify AWS resources with Amazon Resource Names (ARNs).

  • Optional: parameters.iopsPerGB. Only for io1 volumes. I/O operations per second per GiB.

    The AWS volume plugin multiplies this with the size of the requested volume to compute IOPS of the volume. The maximum value is 20,000 IOPS, which is the maximum supported by AWS.

    For more information, see the AWS documentation, Identify AWS resources with Amazon Resource Names (ARNs).

  • Optional: parameters.encrypted. Indicates whether to encrypt the EBS volume. Valid values are true or false.

  • Optional: parameters.kmsKeyId. The full ARN of the key to use when encrypting the volume. If none is supplied, but encypted is set to true, then AWS generates a key.

    For valid ARN values, see the AWS documentation, Identify AWS resources with Amazon Resource Names (ARNs).

  • Optional: parameters.fsType. File system that is created on dynamically provisioned volumes. This value is copied to the fsType field of dynamically provisioned persistent volumes, and the file system is created when the volume is mounted for the first time. The default value is ext4.

9.3.5. Azure Disk StorageClass object definition
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This Azure Disk storage class example demonstrates how to configure managed disks with delayed volume binding for optimal zone placement, volume expansion, and performance tiers. Key parameters ensure compatibility with OpenShift nodes, which require managed disks rather than shared or dedicated storage accounts.

Example Azure Disk storage class YAML file

apiVersion: storage.k8s.io/v1
kind: StorageClass
metadata:
  name: <storage-class-name>
provisioner: kubernetes.io/azure-disk
volumeBindingMode: WaitForFirstConsumer
allowVolumeExpansion: true
parameters:
  kind: Managed
  storageaccounttype: Premium_LRS
reclaimPolicy: Delete

  • metadata.name: Name of the storage class. The persistent volume claim uses this storage class for provisioning the associated persistent volumes.
  • volumeBindingMode: Using WaitForFirstConsumer is strongly recommended. This provisions the volume while allowing enough storage to schedule the pod on a free worker node from an available zone.

  • parameters.kind: Possible values are Shared (default), Managed, and Dedicated.

    Important

    Red Hat only supports the use of Managed.

    With Shared and Dedicated, Azure creates unmanaged disks, while OpenShift Container Platform creates a managed disk for machine operating system (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 OpenShift Container Platform nodes.

  • parameters.storageaccounttype: Azure storage account SKU tier. Default is empty. Note that Premium VMs can attach both Standard_LRS and Premium_LRS disks. Standard VMs can only attach Standard_LRS disks. Managed VMs can only attach managed disks. Unmanaged VMs can only attach unmanaged disks.

    • Shared: Azure creates all unmanaged disks in a few shared storage accounts in the same resource group as the cluster.
    • Managed: Azure creates new managed disks.
    • Dedicated, and a storageAccount is not specified: Azure creates a new dedicated storage account for the new unmanaged disk in the same resource group as the cluster.
    • Dedicated, and a storageAccount is specified: Azure uses the specified storage account for the new unmanaged disk in the same resource group as the cluster. For this to work, the specified storage account must be in the same region, and Azure Cloud Provider must have write access to the storage account.

9.3.6. Azure File object definition
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To enable Azure File storage classes to dynamically provision file shares, grant the persistent volume binder permissions to create and manage secrets containing Azure storage credentials. This allows the provisioner to securely store and access the Azure storage account name and key required for file share creation.

Procedure

  1. Define a ClusterRole object that allows access to create and view secrets as in the following example file:

    Cluster role example YAML file

    apiVersion: rbac.authorization.k8s.io/v1
kind: ClusterRole
metadata:
  name: <persistent_volume_binder_role>
rules:
- apiGroups: ['']
  resources: ['secrets']
  verbs:     ['get','create']

    • Metadata.name: The name of the cluster role to view and create secrets.

  2. Add the cluster role to the service account by running the following command: 

    $ oc adm policy add-cluster-role-to-user <persistent-volume-binder-role> system:serviceaccount:kube-system:persistent-volume-binder

    Where <persistent-volume-binder-role> is the name of the cluster role you provided in the preceding step.

  3. Create the Azure File StorageClass object as in the following example file:

    Example Azure File storage class YAML file

    kind: StorageClass
apiVersion: storage.k8s.io/v1
metadata:
  name: <azure-file>
provisioner: kubernetes.io/azure-file
parameters:
  location: eastus
  skuName: Standard_LRS
  storageAccount: <storage-account>
reclaimPolicy: Delete
volumeBindingMode: Immediate

    • metadata.name: Name of the storage class. The persistent volume claim uses this storage class for provisioning the associated persistent volumes.
    • parameters.location: Location of the Azure storage account, such as eastus. The default is empty, meaning that a new Azure storage account is created in the OpenShift Container Platform cluster’s location.
    • parameters.skuName: SKU tier of the Azure storage account, such as Standard_LRS. The default is empty, meaning that a new Azure storage account is created with the Standard_LRS SKU.
    • parameters.storageAccount: Name of the Azure storage account. If a storage account is provided, then skuName and location are ignored. If no storage account is provided, the storage class searches for storage accounts associated with the resource group for accounts that match the defined skuName and location.

9.3.6.1. Considerations when using Azure File
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Azure File storage has inherent file system limitations, including lack of support for symlinks, hard links, and sparse files by default, plus ownership mismatches between mounted directories and container processes. Understanding these constraints and using mount options such as uid, gid, and mfsymlinks helps you configure Azure File storage classes that work correctly with your containerized applications.

The following features are not supported:

  • Symlinks
  • Hard links
  • Extended attributes
  • Sparse files
  • Named pipes

Additionally, the owner user identifier (UID) of the Azure File mounted directory is different from the process UID of the container. You can specify the uid mount option in the StorageClass object to define a specific user identifier to use for the mounted directory.

The following StorageClass object demonstrates modifying the uid and group identifier (gid), along with enabling symlinks for the mounted directory.

Example Azure File storage class YAML file with modified uid and gid

kind: StorageClass
apiVersion: storage.k8s.io/v1
metadata:
  name: azure-file
mountOptions:
  - uid=1500
  - gid=1500
  - mfsymlinks
provisioner: kubernetes.io/azure-file
parameters:
  location: eastus
  skuName: Standard_LRS
reclaimPolicy: Delete
volumeBindingMode: Immediate

  • mountOptions.uid: Specifies the user identifier to use for the mounted directory.
  • mountOptions.gid: Specifies the group identifier to use for the mounted directory.
  • mountOptions.mfsymlinks: Enables symlinks.

9.3.7. GCE PersistentDisk (gcePD) object definition
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This Google Compute Engine Persistent Disk (GCE PD) storage class example shows how to configure disk performance tiers (SSD, standard, or hyperdisk-balanced), enable volume expansion, and use delayed binding to optimize zone placement for your workloads.

Example GCE PD storage class YAML file

apiVersion: storage.k8s.io/v1
kind: StorageClass
metadata:
  name: <storage-class-name>
provisioner: kubernetes.io/gce-pd
parameters:
  type: pd-ssd
  replication-type: none
volumeBindingMode: WaitForFirstConsumer
allowVolumeExpansion: true
reclaimPolicy: Delete

  • metadata.name: The name of the storage class. The persistent volume claim uses this storage class for provisioning the associated persistent volumes.
  • parameters.type: Select pd-ssd, pd-standard, or hyperdisk-balanced. The default is pd-ssd.

9.3.8. VMware vSphere object definition
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This VMware vSphere storage class example demonstrates the basic structure and Container Storage Interface (CSI) provisioner configuration required to enable dynamic storage provisioning on vSphere infrastructure. This minimal definition provides the foundation for vSphere storage integration, which you can extend with storage policies, datastore preferences, and other vSphere-specific parameters.

Example vSphere storage class YAML file

kind: StorageClass
apiVersion: storage.k8s.io/v1
metadata:
  name: <storage-class-name>
1 

provisioner: csi.vsphere.vmware.com
2

  • metadata.name: Name of the storage class. The persistent volume claim uses this storage class for provisioning the associated persistent volumes.
  • provisioner: The name of the provisioner for the storage class. For vSphere, this is csi.vsphere.vmware.com.

9.4. Setting the default storage class
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A default storage class automatically provisions persistent volumes when you create persistent volume claims (PVCs) without specifying a storage class. This simplifies storage management by removing the need for users to select a storage class for each claim. To designate a storage class as the cluster-wide default, add an annotation to the storage class metadata.

Prerequisites

  • Logged in to a running OpenShift Container Platform cluster with administrator privileges.

Procedure

  1. For your required storage class, set the metadata.annotations.storageclass.kubernetes.io/is-default-class field to true as in the following example:

    Example storage class YAML file

    apiVersion: storage.k8s.io/v1
kind: StorageClass
metadata:
  annotations:
    storageclass.kubernetes.io/is-default-class: "true"
...

    Note

    The beta annotation storageclass.beta.kubernetes.io/is-default-class is still working; however, it will be removed in a future release.

  2. Optional: Create a storage class description in the metadata.annotations.kubernetes.io/description field as in the following example:

    Example storage class YAML file

    apiVersion: storage.k8s.io/v1
kind: StorageClass
metadata:
  annotations:
    kubernetes.io/description: My Storage Class Description
...

9.5. Changing the default storage class
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Change the default storage class to ensure new persistent volume claims (PVCs) automatically use your preferred storage backend. This helps you optimize costs, align with infrastructure changes, or ensure consistent storage types across new deployments without requiring users to specify a storage class for each claim.

In this example, you have two defined storage classes, gp3 and standard, and you want to change the default storage class from gp3 to standard.

Prerequisites

  • Access to the cluster with cluster-admin privileges.

Procedure

  1. List the storage classes by running the following command: 

    $ oc get storageclass

    Example output

    NAME                 TYPE
gp3 (default)        ebs.csi.aws.com
standard             ebs.csi.aws.com

    The text (default) indicates the default storage class. In this example gp3 is the current default storage class.

  2. Make the required storage class the default.

    For the required storage class, set the storageclass.kubernetes.io/is-default-class annotation to true by running the following command: 

    $ oc patch storageclass standard -p '{"metadata": {"annotations": {"storageclass.kubernetes.io/is-default-class": "true"}}}'
    Note

    You can have many default storage classes for a short time. However, you must ensure that only one default storage class exists eventually.

    With many default storage classes present, any persistent volume claim (PVC) requesting the default storage class (pvc.spec.storageClassName=nil) gets the most recently created default storage class, regardless of the default status of that storage class. The administrator receives an alert in the alerts dashboard that there are many default storage classes, MultipleDefaultStorageClasses.

  3. Remove the default storage class setting from the old default storage class.

    For the old default storage class, change the value of the storageclass.kubernetes.io/is-default-class annotation to false by running the following command: 

    $ oc patch storageclass gp3 -p '{"metadata": {"annotations": {"storageclass.kubernetes.io/is-default-class": "false"}}}'

  4. Verify the changes by running the following command: 

    $ oc get storageclass

    Example output

    NAME                 TYPE
gp3                  ebs.csi.aws.com
standard (default)   ebs.csi.aws.com

    The standard storage class is now the default.

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