Updated on 2024-01-26 GMT+08:00

Using a Local PV Through a Dynamic PV

Prerequisites

Constraints

  • Local PVs are supported only when the cluster version is v1.21.2-r0 or later and the everest add-on version is 2.1.23 or later. Version 2.1.23 or later is recommended.
  • Deleting, removing, resetting, or scaling in a node will cause the PVC/PV data of the local PV associated with the node to be lost, which cannot be restored or used again. For details, see Removing a Node, Deleting a Node, Resetting a Node, and Scaling a Node. In these scenarios, the pod that uses the local PV is evicted from the node. A new pod will be created and stay in the pending state. This is because the PVC used by the pod has a node label, due to which the pod cannot be scheduled. After the node is reset, the pod may be scheduled to the reset node. In this case, the pod remains in the creating state because the underlying logical volume corresponding to the PVC does not exist.
  • Do not manually delete the corresponding storage pool or detach data disks from the node. Otherwise, exceptions such as data loss may occur.
  • A local PV cannot be mounted to multiple workloads or jobs at the same time.

Automatically Creating a Local PV on the Console

  1. Log in to the CCE console and click the cluster name to access the cluster console.
  2. Dynamically create a PVC and PV.

    1. Choose Storage from the navigation pane, and click the PersistentVolumeClaims (PVCs) tab. Click Create PVC in the upper right corner. In the dialog box displayed, configure the PVC parameters.

      Parameter

      Description

      PVC Type

      In this section, select Local PV.

      PVC Name

      Enter the PVC name, which must be unique in the same namespace.

      Creation Method

      You can only select Dynamically provision to create a PVC, PV, and underlying storage on the console in cascading mode.

      Storage Classes

      The storage class of local PVs is csi-local-topology.

      Access Mode

      Local PVs support only ReadWriteOnce, indicating that a storage volume can be mounted to one node in read/write mode. For details, see Volume Access Modes.

      Storage Pool

      View the imported storage pool. For details about how to import a new data volume to the storage pool, seeImporting a PV to a Storage Pool.

      Capacity (GiB)

      Capacity of the requested storage volume.

    2. Click Create to create a PVC and a PV.

      You can choose Storage in the navigation pane and view the created PVC and PV on the PersistentVolumeClaims (PVCs) and PersistentVolumes (PVs) tab pages.

      The volume binding mode of the local storage class (named csi-local-topology) is late binding (that is, the value of volumeBindingMode is WaitForFirstConsumer). In this mode, PV creation and binding are delayed. The corresponding PV is created and bound only when the PVC is used during workload creation.

  3. Create an application.

    1. In the navigation pane on the left, click Workloads. In the right pane, click the Deployments tab.
    2. Click Create Workload in the upper right corner. On the displayed page, click Data Storage in the Container Settings area and click Add Volume to select PVC.
      Mount and use storage volumes, as shown in Table 1. For details about other parameters, see Workloads.
      Table 1 Mounting a storage volume

      Parameter

      Description

      PVC

      Select an existing local PV.

      A local PV cannot be repeatedly mounted to multiple workloads.

      Mount Path

      Enter a mount path, for example, /tmp.

      This parameter indicates the container path to which a data volume will be mounted. Do not mount the volume to a system directory such as / or /var/run. Otherwise, containers will be malfunctional. Mount the volume to an empty directory. If the directory is not empty, ensure that there are no files that affect container startup. Otherwise, the files will be replaced, causing container startup failures or workload creation failures.
      NOTICE:

      If a volume is mounted to a high-risk directory, use an account with minimum permissions to start the container. Otherwise, high-risk files on the host machine may be damaged.

      Subpath

      Enter a subpath, for example, tmp, indicating that data in the mount path of the container will be stored in the tmp folder of the volume.

      A subpath is used to mount a local volume so that the same data volume is used in a single pod. If this parameter is left blank, the root path is used by default.

      Permission

      • Read-only: You can only read the data in the mounted volumes.
      • Read/Write: You can modify the data volumes mounted to the path. Newly written data is not migrated if the container is migrated, which may cause data loss.

      In this example, the disk is mounted to the /data path of the container. The container data generated in this path is stored in the local PV.

    3. After the configuration, click Create Workload.

      After the workload is created, the data in the container mount directory will be persistently stored. Verify the storage by referring to Verifying Data Persistence.

(kubectl) Automatically Creating a Local PV

  1. Use kubectl to connect to the cluster.
  2. Use StorageClass to dynamically create a PVC and PV.

    1. Create the pvc-local.yaml file.
      apiVersion: v1
      kind: PersistentVolumeClaim
      metadata:
        name: pvc-local
        namespace: default
      spec:
        accessModes:
          - ReadWriteOnce             # The local PV must adopt ReadWriteOnce.
        resources:
          requests:
            storage: 10Gi             # Size of the local PV.
        storageClassName: csi-local-topology    # StorageClass is local PV.
      Table 2 Key parameters

      Parameter

      Mandatory

      Description

      storage

      Yes

      Requested capacity in the PVC, in Gi.

      storageClassName

      Yes

      Storage class name. The storage class name of local PV is csi-local-topology.

    2. Run the following command to create a PVC:
      kubectl apply -f pvc-local.yaml

  3. Create an application.

    1. Create a file named web-demo.yaml. In this example, the local PV is mounted to the /data path.
      apiVersion: apps/v1
      kind: StatefulSet
      metadata:
        name: web-local
        namespace: default
      spec:
        replicas: 1
        selector:
          matchLabels:
            app: web-local
        serviceName: web-local   # Headless Service name.
        template:
          metadata:
            labels:
              app: web-local
          spec:
            containers:
            - name: container-1
              image: nginx:latest
              volumeMounts:
              - name: pvc-disk    #Volume name, which must be the same as the volume name in the volumes field.
                mountPath: /data  #Location where the storage volume is mounted.
            imagePullSecrets:
              - name: default-secret
            volumes:
              - name: pvc-disk    #Volume name, which can be customized.
                persistentVolumeClaim:
                  claimName: pvc-local    #Name of the created PVC.
      ---
      apiVersion: v1
      kind: Service
      metadata:
        name: web-local   # Headless Service name.
        namespace: default
        labels:
          app: web-local
      spec:
        selector:
          app: web-local
        clusterIP: None
        ports:
          - name: web-local
            targetPort: 80
            nodePort: 0
            port: 80
            protocol: TCP
        type: ClusterIP
    2. Run the following command to create an application to which the local PV is mounted:
      kubectl apply -f web-local.yaml

      After the workload is created, the data in the container mount directory will be persistently stored. Verify the storage by referring to Verifying Data Persistence.

Verifying Data Persistence

  1. View the deployed application and local files.

    1. Run the following command to view the created pod:
      kubectl get pod | grep web-local
      Expected output:
      web-local-0                  1/1     Running   0               38s
    2. Run the following command to check whether the local PV has been mounted to the /data path:
      kubectl exec web-local-0 -- df | grep data

      Expected output:

      /dev/mapper/vg--everest--localvolume--persistent-pvc-local          10255636     36888  10202364   0% /data
    3. Run the following command to view the files in the /data path:
      kubectl exec web-local-0 -- ls /data

      Expected output:

      lost+found

  2. Run the following command to create a file named static in the /data path:

    kubectl exec web-local-0 --  touch /data/static

  3. Run the following command to view the files in the /data path:

    kubectl exec web-local-0 -- ls /data

    Expected output:

    lost+found
    static

  4. Run the following command to delete the pod named web-local-0:

    kubectl delete pod web-local-0

    Expected output:

    pod "web-local-0" deleted

  5. After the deletion, the StatefulSet controller automatically creates a replica with the same name. Run the following command to check whether the files in the /data path have been modified:

    kubectl exec web-local-0 -- ls /data

    Expected output:

    lost+found
    static

    If the static file still exists, the data in the local PV can be stored persistently.

Related Operations

You can also perform the operations listed in Table 3.
Table 3 Related operations

Operation

Description

Procedure

Viewing events

You can view event names, event types, number of occurrences, Kubernetes events, first occurrence time, and last occurrence time of the PVC or PV.

  1. Choose Storage from the navigation pane, and click the PersistentVolumeClaims (PVCs) or PersistentVolumes (PVs) tab.
  2. Click View Events in the Operation column of the target PVC or PV to view events generated within one hour (event data is retained for one hour).

Viewing a YAML file

You can view, copy, and download the YAML files of a PVC or PV.

  1. Choose Storage from the navigation pane, and click the PersistentVolumeClaims (PVCs) or PersistentVolumes (PVs) tab.
  2. Click View YAML in the Operation column of the target PVC or PV to view or download the YAML.