Persistent Volume Claims

When you create an application workload in a project, you can create a Persistent Volume Claim (PVC) for it. A PVC allows you to create a storage request, further provisioning persistent storage to applications. More specifically, persistent storage is managed by persistent volume resources.

Cluster administrators configure Persistent Volumes (PVs) using storage classes. In other words, to create a PVC in a project, your cluster must have an available storage class. If no customized storage class is configured when you install KubeSphere, OpenEBS is installed in your cluster by default to provide local persistent volumes. However, it does not support dynamic volume provisioning. In a production environment, it is recommended you configure storage classes in advance to provide persistent storage services for your apps.

This tutorial demonstrates how to create a PVC, mount a PVC, and use PVC features from its details page.

Prerequisites

• You need to create a workspace, a project and a user (project-regular). The user must be invited to the project with the role of operator. For more information, see Create Workspaces, Projects, Users and Roles.

• If you want to dynamically provision a volume, you need to configure a storage class that supports dynamic provisioning.

Create a PVC

KubeSphere binds a PVC to a PV that satisfies the request you set for the PVC, such as capacity and access mode. When you create an application workload, you can select the desired PVC and mount it to your workload.

1. Log in to the web console of KubeSphere as project-regular and go to a project. Click Persistent Volume Claims under Storage from the navigation bar, and you see all PVCs that have been mounted to workloads in the project.

2. To create a PVC, click Create on the Persistent Volume Claims page.

3. In the displayed dialog box, set a name (for example, demo-volume) for the PVC, select a project, and click Next.

   Note

   You can see the PVC's manifest file in YAML format by enabling Edit YAML in the upper-right corner. You can edit the manifest file directly to create a PVC. Alternatively, you can follow the steps below to create a PVC using the console.

4. On the Storage Settings page, select a method to create a PVC.

   • From Storage Class. You can configure storage classes both before and after the installation of KubeSphere.

   • From Volume Snapshot. To use a snapshot to create a PVC, you must create a volume snapshot first.

   Select From Storage Class in this example. For more information about how to create a PVC by snapshot, see Volume Snapshots.

5. Select a storage class from the drop-down list. This tutorial uses csi-standard, a standard storage class provided by QingCloud Platform. You can select your own storage class.

6. Depending on the storage class you select, you may see different access modes in this section as some PVs only support specific access modes. In total, there are three access modes.

   • ReadWriteOnce: The volume can be mounted as read-write by a single node.
   • ReadOnlyMany: The volume can be mounted as read-only by many nodes.
   • ReadWriteMany: The volume can be mounted as read-write by many nodes.

   Select the desired access mode.

7. Under Volume Capacity, specify the size of the PVC. Click Next to continue.

8. On the Advanced Settings page, you can add metadata to the PVC, such as Labels and Annotations. They can be used as identifiers to search for and schedule resources.

9. Click Create to finish creating a PVC.

10. A created PVC displays on the Persistent Volume Claims page in a project. After it is mounted to a workload, it will turn to Mounted under the Mount Status column.

    Note

    Newly-created PVCs are also displayed on the Persistent Volume Claims page in Cluster Management. Project users such as project-regular can view PVs under the Persistent Volumes column. Cluster administrators have the responsibility to view and keep track of created PVCs in a project. Conversely, if a cluster administrator creates a PVC for a project in Cluster Management, the PVC is also displayed on the Persistent Volume Claims page in a project.

Mount a PVC

When you create application workloads, such as Deployments, StatefulSets and DaemonSets, you can mount PVCs to them.

On the Storage Settings page, you can see there are different volumes that you can mount to your workload.

• Add Persistent Volume Claim Template (Only available to StatefulSets): A PVC template is used to dynamically create a PVC. Mount the PVC of the StorageClass type to the Pod by setting the name, storage class, access mode, capacity and path, which are all indicated by the field volumeClaimTemplates.

• Mount Volume: Support emptyDir volumes and PVCs.

  In Mount Volume, there are three kinds of volumes:

  • Persistent Volume: Use a PVC to mount.

    Persistent volumes can be used to save users' persistent data. You need to create PVCs in advance so that you can choose an existing PVC from the list.

  • Temporary Volume: Use an emptyDir volume to mount.

    The temporary volume represents emptyDir, which is first created when a Pod is assigned to a node, and exists as long as that Pod is running on that node. An emptyDir volume offers an empty directory from which containers in the Pod can read and write. Depending on your deployment environment, an emptyDir volume can be stored on any medium that is backing the node, which could be a disk or SSD. When the Pod is removed from the node for any reason, the data in the emptyDir is deleted forever.

  • HostPath Volume: Use a hostPath volume to mount.

    A HostPath volume mounts a file or directory from the host node's filesystem into your Pod. This is not something that most Pods will need, but it offers a powerful escape hatch for some applications. For more information, refer to the Kubernetes documentation.

• Mount ConfigMap or Secret: Support key-value pairs of ConfigMaps or Secrets.

  A Secret volume is used to provide sensitive information, such as passwords, OAuth tokens, and SSH keys, for Pods. Secret volumes are backed by tmpfs (a RAM-backed filesystem) so they are never written to non-volatile storage.

  A ConfigMap is used to store configuration data in the form of key-value pairs. The ConfigMap resource provides a way to inject configuration data into Pods. The data stored in a ConfigMap object can be referenced in a volume of type configMap and then consumed by containerized applications running in a Pod. ConfigMaps are often used in the following cases:

  • Set the value of environment variables.
  • Set command parameters in containers.
  • Create a configuration file in volumes.

View and Manage PVCs

After a PVC is created, you can see detailed information of it, edit it, or leverage PVC features. To view PVC details, click a PVC on the Persistent Volume Claims page.

View Details of a PVC

On the Persistent Volume Claims page, click a PVC to view its details.

1. Click the Resource Status tab, view the PVC usage and mounted pods.

2. Click the Metadata tab, view the labels and annotations of the PVC.

3. Click the Events tab, view the events of the PVC.

4. Click the Snapshots tab, view the snapshots of the PVC.

Edit a PVC

On the details page, you can click Edit Information to change its basic information. Click More, and you can edit its YAML file or delete this PVC.

To delete a PVC, make sure the PVC is not mounted to any workload. To unmount a PVC, go to the details page of a workload. From the More drop-down list, click Edit Settings. On the Edit Settings dialog box, click Storage. Hover your mouse on the PVC, and click the dustbin icon to unmount it.

If the status of a PVC remains Terminating for a long time after you clicked Delete, manually delete it by using the following command:

kubectl patch pvc <pvc-name> -p '{"metadata":{"finalizers":null}}'

Use PVC Features

From the More drop-down menu, there are other additional options provided by KubeSphere based on the underlying storage plugin, also known as Storage Capability. PVC features include the following:

• Clone: Create a same PVC.
• Create Snapshot: Create a volume snapshot which can be used to create PVCs. For more information, see Volume Snapshots.
• Expand: Increase the size of a PVC. Keep in mind that you cannot reduce the size of a PVC on the console due to possible data loss.

For more information about Storage Capability, see Design Documentation.

Monitor PVCs

KubeSphere retrieves metric data of PVCs with Filesystem mode from Kubelet to monitor PVCs including capacity usage and inode usage.

For more information about PVC monitoring, see Research on Volume Monitoring.

View the PV List and Manage PVs

View the PV List

1. Click the Persistent Volumes tab on the Persistent Volume Claims page to view the PV list page that provides the following information:

   Parameter	Description
   Name	Name of the PV. It is specified by the field .metadata.name in the manifest file of the PV.
   Status	Current status of the PV. It is specified by the field .status.phase in the manifest file of the PV, including: Available: The PV is available and not yet bound to a PVC. Bound: The PV is bound to a PVC. Deleting: The PV is being deleted. Failed: The PV is unavailable.
   Capacity	Capacity of the PV. It is specified by the field .spec.capacity.storage in the manifest file of the PV.
   Access Mode	Access mode of the PV. It is specified by the field .spec.accessModes in the manifest file of the PV, including: RWO: The PV can be mounted as read-write by a single node. ROX: The PV can be mounted as read-only by multiple nodes. RWX: The PV can be mounted as read-write by multiple nodes.
   Reclaim Policy	Reclaim policy of the PV. It is specified by the field .spec.persistentVolumeReclaimPolicy in the manifest file of the PV, including: Retain: When a PVC is deleted, the PV still exists and requires manual reclamation. Delete: Remove both the PV and the associated storage assets in the volume plugin infrastructure. Recycle: Erase the data on the PV and make it available again for a new PVC.
   Creation Time	Time when the PV was created.

2. Click on the right of a PV, and you can perform the following:

   • Edit Information: Edit information of the PV.
   • Edit YAML: Edit the YAML file of the PV.
   • Delete: Delete the PV. A PV in the Bound status cannot be deleted.

View the PV Details Page

1. Click the name of a PV to go to its details page.

2. On the details page, click Edit Information to edit the basic information of the PV.

3. Click More, and you can perform the following:

   • View YAML: View the YAML file of the PV.
   • Delete: Delete the PV and return to the list page. A PV in the Bound status cannot be deleted.

4. Click the Resource Status tab to view the PVC to which the PV is bound.

5. Click the Metadata tab to view the labels and annotations of the PV.

6. Click the Events tab to view the events of the PV.

Thanks for the feedback. If you have a specific question about how to use KubeSphere, ask it on Slack. Open an issue in the GitHub repo if you want to report a problem or suggest an improvement.