Using pre-existing persistent disks as PersistentVolumes

Autopilot Standard

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This page explains how to create a PersistentVolume using existing persistent disks populated with data, and how to use the PersistentVolume in a Pod.

Overview

There are two common scenarios which use a pre-existing persistent disk.

• Manually creating a PersistentVolumeClaim and a PersistentVolume, binding them together, and referring to the PersistentVolumeClaim in a Pod specification.
• Use a StatefulSet to automatically generate PersistentVolumeClaims which are bound to manually generated PersistentVolumes corresponding to a series of pre-existing persistent disks.

The examples in this page use existing Compute Engine persistent disks.

While ext4 is the default filesystem type, you can use a pre-existing persistent disk with the xfs filesystem instead as long as your node image supports it. To use an xfs disk, change spec.csi.fsType to xfs in the PersistentVolume manifest.

Windows does not support the ext4 filesystem type. You must use the NTFS filesystem for Windows Server node pools. To use an NTFS disk, change spec.csi.fsType to NTFS in the PersistentVolume manifest.

Note: If the filesystem type for the persistent disk you use doesn't match the fsType you specify in the PersistentVolume manifest, pods you create that consume the volumes will not start, and you will see errors in the Pod description. Similarly, Persistent Disk CSI volumes only support a single partition. Volumes created outside of GKE with multiple partitions cannot be used with this technique.

Before you begin

Before you start, make sure you have performed the following tasks:

• Enable the Google Kubernetes Engine API.
Enable Google Kubernetes Engine API
• If you want to use the Google Cloud CLI for this task, install and then initialize the gcloud CLI. If you previously installed the gcloud CLI, get the latest version by running gcloud components update.
  Note: For existing gcloud CLI installations, make sure to set the compute/region and compute/zone properties. By setting default locations, you can avoid errors in gcloud CLI like the following: One of [--zone, --region] must be supplied: Please specify location.

• Ensure that you have existing persistent disks. To provision a disk, see Provisioning regional persistent disks.
• Ensure that your cluster uses the Compute Engine persistent disk CSI driver.

Using a PersistentVolumeClaim bound to the PersistentVolume

For a container to access your pre-existing persistent disk, you'll need to do the following:

1. Provision the existing persistent disk as a PersistentVolume.
2. Bind the PersistentVolume to a PersistentVolumeClaim.
3. Give the containers in the Pod access to the PersistentVolume.

Create the PersistentVolume and PersistentVolumeClaim

There are several ways to bind a PersistentVolumeClaim to a specific PersistentVolume. For example, the following YAML manifest creates a new PersistentVolume and PersistentVolumeClaim, and then binds the claim to the volume using volumeName.

To bind a PersistentVolume to a PersistentVolumeClaim, the storageClassName of the two resources must match, as well as capacity, accessModes, and volumeMode. You can omit the storageClassName, but you must specify "" to prevent Kubernetes from using the default StorageClass.

The storageClassName does not need to refer to an existing StorageClass object. If all you need is to bind the claim to a volume, you can use any name you want. However, if you need extra functionality configured by a StorageClass, like volume resizing, then storageClassName must refer to an existing StorageClass object.

For more details, see the Kubernetes documentation on PersistentVolumes.

Note: The persistent disk must be in the same zone as the cluster nodes.

1. Save the following YAML manifest:

   apiVersion: v1
   kind: PersistentVolume
   metadata:
     name: PV_NAME
   spec:
     storageClassName: "STORAGE_CLASS_NAME"
     capacity:
       storage: DISK_SIZE
     accessModes:
       - ReadWriteOnce
     csi:
       driver: pd.csi.storage.gke.io
       volumeHandle: DISK_ID
       fsType: FS_TYPE
   ---
   apiVersion: v1
   kind: PersistentVolumeClaim
   metadata:
     namespace: default
     name: PV_CLAIM_NAME
   spec:
     storageClassName: "STORAGE_CLASS_NAME"
     volumeName: PV_NAME
     accessModes:
       - ReadWriteOnce
     resources:
       requests:
         storage: DISK_SIZE
   

   Replace the following:

   • PV_NAME: the name of your new PersistentVolume.
   • STORAGE_CLASS_NAME: the name of your new StorageClass.
   • DISK_SIZE: the size of your pre-existing persistent disk. For example, 500G.
   • PV_CLAIM_NAME: the name of your new PersistentVolumeClaim.
   • DISK_ID: the identifier of your pre-existing persistent disk. The format is projects/{project_id}/zones/{zone_name}/disks/{disk_name} for Zonal persistent disks, or projects/{project_id}/regions/{region_name}/disks/{disk_name} for Regional persistent disks.
   • FS_TYPE: the filesystem type. You can leave this as the default (ext4), or use xfs. If your clusters use a Windows Server node pool, you must change this to NTFS.

2. To apply the configuration and create the PersistentVolume and PersistentVolumeClaim resources, run the following command:

   kubectl apply -f FILE_PATH
   

   Replace FILE_PATH with the path to the YAML file.

Use the PersistentVolume in a Pod

After you create and bind the PersistentVolume and PersistentVolumeClaim, you can give a Pod's containers access to the volume by specifying values in the volumeMounts field.

The following YAML configuration creates a new Pod and a container running an nginx image, and then mounts the PersistentVolume on the Pod:

kind: Pod
apiVersion: v1
metadata:
  name: POD_NAME
spec:
  volumes:
    - name: VOLUME_NAME
      persistentVolumeClaim:
        claimName: PV_CLAIM_NAME
  containers:
    - name: CONTAINER_NAME
      image: nginx
      ports:
        - containerPort: 80
          name: "http-server"
      volumeMounts:
        - mountPath: "/usr/share/nginx/html"
          name: VOLUME_NAME

Replace the following:

• POD_NAME: the name of your new Pod.
• VOLUME_NAME: the name of the volume.
• PV_CLAIM_NAME: the name of the PersistentVolumeClaim you created in the previous step.
• CONTAINER_NAME: the name of your new container.

Apply the configuration:

kubectl apply -f FILE_PATH

Replace FILE_PATH with the path to the YAML file.

To verify that the volume was mounted, run the following command:

kubectl describe pods POD_NAME

In the output, check that the PersistentVolumeClaim was mounted:

...
Volumes:
  VOLUME_NAME:
    Type:       PersistentVolumeClaim (a reference to a PersistentVolumeClaim in the same namespace)
    ClaimName:  PV_CLAIM_NAME
    ReadOnly:   false
Events:
  Type    Reason                  Age   From                     Message
  ----    ------                  ----  ----                     -------
  Normal  Scheduled               29s   default-scheduler        Successfully assigned default/POD_NAME to gke-cluster-1-default-pool-d5cde866-o4g4
  Normal  SuccessfulAttachVolume  21s   attachdetach-controller  AttachVolume.Attach succeeded for volume "PV_NAME"
  Normal  Pulling                 19s   kubelet                  Pulling image "nginx"
  Normal  Pulled                  19s   kubelet                  Successfully pulled image "nginx"
  Normal  Created                 18s   kubelet                  Created container CONTAINER_NAME
  Normal  Started                 18s   kubelet                  Started container CONTAINER_NAME

Using a pre-existing disk in a StatefulSet

You can use pre-existing Compute Engine persistent disks in a StatefulSet using PersistentVolumes. The StatefulSet automatically generates a PersistentVolumeClaim for each replica. You can predict the names of the generated PersistentVolumeClaims and bind them to the PersistentVolumes using claimRef.

In the following example, you take two pre-existing persistent disks, create PersistentVolumes to use the disks, and then mount the volumes on a StatefulSet with two replicas in the default namespace.

1. Decide on a name for your new StatefulSet, a name for your PersistentVolumeClaim template, and the number of replicas in the StatefulSet.

2. Work out the names of the automatically generated PersistentVolumeClaims. The StatefulSet uses the following format for PersistentVolumeClaim names:

   PVC_TEMPLATE_NAME-STATEFULSET_NAME-REPLICA_INDEX
   

   Replace the following:

   • PVC_TEMPLATE_NAME: the name of your new PersistentVolumeClaim template.
   • STATEFULSET_NAME: the name of your new StatefulSet.
   • REPLICA_INDEX: the index of the StatefulSet's replica. For this example, use 0 and 1.

3. Create the PersistentVolumes. You must create a PersistentVolume for each replica in the StatefulSet.

   1. Save the following YAML manifest:

      apiVersion: v1
      kind: PersistentVolume
      metadata:
        name: pv-ss-demo-0
      spec:
        storageClassName: "STORAGE_CLASS_NAME"
        capacity:
          storage: DISK1_SIZE
        accessModes:
          - ReadWriteOnce
        claimRef:
          namespace: default
          name: PVC_TEMPLATE_NAME-STATEFULSET_NAME-0
        csi:
          driver: pd.csi.storage.gke.io
          volumeHandle: DISK1_ID
          fsType: FS_TYPE
       ---
      apiVersion: v1
      kind: PersistentVolume
      metadata:
        name: pv-ss-demo-1
      spec:
        storageClassName: "STORAGE_CLASS_NAME"
        capacity:
          storage: DISK2_SIZE
        accessModes:
          - ReadWriteOnce
        claimRef:
          namespace: default
          name: PVC_TEMPLATE_NAME-STATEFULSET_NAME-1
        csi:
          driver: pd.csi.storage.gke.io
          volumeHandle: DISK2_ID
          fsType: FS_TYPE
      

      Replace the following:

      • DISK1_SIZE and DISK2_SIZE: the sizes of your pre-existing persistent disks.
      • DISK1_ID and DISK2_ID: the identifiers of your pre-existing persistent disks.
      • PVC_TEMPLATE_NAME-STATEFULSET_NAME-0 and PVC_TEMPLATE_NAME-STATEFULSET_NAME-1: the names of the automatically generated PersistentVolumeClaims in the format defined in the previous step.
      • STORAGE_CLASS_NAME: the name of your StorageClass.

   2. Apply the configuration:

      kubectl apply -f FILE_PATH
      

      Replace FILE_PATH with the path to the YAML file.

4. Create a StatefulSet using the values you chose in step 1. Ensure that the storage you specify in the volumeClaimTemplates is less than or equal to the total capacity of your PersistentVolumes.

   1. Save the following YAML manifest:

      apiVersion: apps/v1
      kind: StatefulSet
      metadata:
        name: STATEFULSET_NAME
      spec:
        selector:
          matchLabels:
            app: nginx
        serviceName: "nginx"
        replicas: 2
        template:
          metadata:
            labels:
              app: nginx
          spec:
            terminationGracePeriodSeconds: 10
            containers:
            - name: nginx
              image: registry.k8s.io/nginx-slim:0.8
              ports:
              - containerPort: 80
                name: web
              volumeMounts:
              - name: PVC_TEMPLATE_NAME
                mountPath: /usr/share/nginx/html
        volumeClaimTemplates:
        - metadata:
            name: PVC_TEMPLATE_NAME
          spec:
            accessModes: [ "ReadWriteOnce" ]
            storageClassName: "STORAGE_CLASS_NAME"
            resources:
              requests:
                storage: 100Gi
      

      Replace the following:

      • STATEFULSET_NAME: the name of your new StatefulSet.
      • PVC_TEMPLATE_NAME: the name of your new PersistentVolumeClaim template.
      • STORAGE_CLASS_NAME: the name of your StorageClass.
      Note: Make sure that your StatefulSet name and PersistentVolumeClaim name match the values you decided in step 1.

   2. Apply the configuration:

      kubectl apply -f FILE_PATH
      

      Replace FILE_PATH with the path to the YAML file.

What's next

• Learn how to deploy a stateful application.