Using a Local PV Through a Dynamic PV

Prerequisites

• You have created a cluster and installed the CSI add-on (Everest) in the cluster.
• To create a cluster using commands, ensure kubectl is used. For details, see Connecting to a Cluster Using kubectl.
• You have imported a data disk of a node to the local PV storage pool. For details, see Importing a PV to a Storage Pool.

Notes and 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, resetting, or scaling a node will cause the loss of the PVC/PV data of the local PV associated with the node. The lost data cannot be restored, and the affected PVC/PV cannot be used again. 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.
• Local PVs are in non-shared mode and cannot be mounted to multiple workloads or tasks concurrently. Additionally, local PVs cannot be mounted to multiple pods of a workload concurrently.

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 in the navigation pane. In the right pane, click the PVCs tab. Click Create PVC in the upper right corner. In the dialog box displayed, configure PVC parameters.

      Parameter	Description
      PVC Type	In this section, select Local PV.
      PVC Name	Enter the PVC name, which must be unique in a 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 default StorageClass of local PVs is csi-local-topology.
      Capacity	Requested capacity of the storage volume in GiB or MiB. NOTE: To implement local PVs, Logical Volume Manager (LVM) is used with a local extent (LE) of 4 MiB. If the requested PVC capacity is not a multiple of 4 MiB, the LVM logical volume's actual capacity will be rounded up to the nearest multiple of 4 MiB. For example, if you request 401 MiB of PVC capacity, the LVM logical volume's actual capacity will be 404 MiB (101 LEs), which is the same as what is displayed on the page.
      Access Mode	Local PVs support only ReadWriteOnce, indicating that a PV 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, see Importing a PV to a Storage Pool.

   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 PVCs and PVs tab pages, respectively.

      

      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. Choose Workloads in the navigation pane. 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 can be mounted to only one workload.
      Mount Path	Enter a mount path, for example, /tmp. This parameter specifies a container path to which a data volume will be mounted. Do not mount the volume to a system directory such as / or /var/run. This may lead to container errors. 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, leading to 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 may be damaged.
      Subpath	Enter the subpath of the storage volume and mount a path in the storage volume to the container. In this way, different folders of the same storage volume can be used in a single pod. tmp, for example, indicates that data in the mount path of the container is stored in the tmp folder of the storage volume. If this parameter is left blank, the root path will be 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 will not be 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.

Automatically Creating a Local PV Through kubectl

1. Use kubectl to access 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 value must be ReadWriteOnce for local PVs.
        resources:
          requests:
            storage: 10Gi             # Local PV capacity
        storageClassName: csi-local-topology    # StorageClass is local PV.

      Table 2 Key parameters

      Parameter	Mandatory	Description
      storage	Yes	Requested PVC capacity in Gi or Mi. NOTE: To implement local PVs, Logical Volume Manager (LVM) is used with a local extent (LE) of 4 MiB. If the requested PVC capacity is not a multiple of 4 MiB, the LVM logical volume's actual capacity will be rounded up to the nearest multiple of 4 MiB. For example, if you request 401 MiB of PVC capacity, the LVM logical volume's actual capacity will be 404 MiB (101 LEs), which is the same as what is displayed on the page.
      storageClassName	Yes	StorageClass name, which is csi-local-topology for a local PV.

   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-local.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 a workload 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 check 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 check 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

   The static file is retained, indicating that the data in the local PV can be stored persistently.

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