Volume lifecycle basics in OCP on bare metal

Summary and Key concepts

Summary:

The article provides instructions for creating and using persistent volumes with the Portworx CSI Driver. It includes examples for defining PersistentVolumeClaim (PVC) specs, such as the px-csi-db storage class, and shows how to reference these PVCs in deployments. It also describes how to create sharedv4 CSI-enabled volumes for multi-pod access, and how to clone volumes using CSI. Lastly, it clarifies that migrating PVCs from Kubernetes' native driver to CSI is not necessary, as both can co-exist in the same cluster.

Kubernetes Concepts:

• PersistentVolumeClaim (PVC): A request for storage resources by a user.
• StorageClass: Defines the class of storage available for dynamically provisioning volumes.
• Deployment: Manages replicated applications, including rolling updates.
• ReadWriteOnce: An access mode where only a single node can mount the volume in read/write mode.
• ReadWriteMany: An access mode where multiple nodes can mount the volume in read/write mode.

Portworx Concepts:

• Portworx CSI Driver: Implements the CSI standard to expose Portworx storage features in Kubernetes.
• Sharedv4 Volumes: Allows multiple pods to share a single volume.
• CSI Volume Cloning: Allows copying a volume, including its data, to create a new volume.

Create and use persistent volumes

Create and use volumes with CSI by configuring specs you create for your storage class, PVC, and volumes.

In this example, we are using the px-csi-db storage class out of the box. Please refer to CSI Enabled Storage Classes for a list of available CSI enabled storage classes offered by Portworx.

1. Create a PersistentVolumeClaim based on the px-csi-db StorageClass:

   kind: PersistentVolumeClaim
   apiVersion: v1
   metadata:
     name: px-mysql-pvc
   spec:
     storageClassName: px-csi-db
     accessModes:
       - ReadWriteOnce
     resources:
       requests:
         storage: 2Gi

2. Create a volume by referencing the PVC you created. This example creates a MySQL deployment referencing the px-mysql-pvc PVC you created in the previous step:

   apiVersion: apps/v1
   kind: Deployment
   metadata:
     name: mysql
   spec:
     selector:
       matchLabels:
         app: mysql
     strategy:
       rollingUpdate:
         maxSurge: 1
         maxUnavailable: 1
       type: RollingUpdate
     replicas: 1
     template:
       metadata:
         labels:
           app: mysql
           version: "1"
       spec:
         containers:
         - image: mysql:5.6
           name: mysql
           env:
           - name: MYSQL_ROOT_PASSWORD
             value: password
           ports:
           - containerPort: 3306
           volumeMounts:
           - name: mysql-persistent-storage
             mountPath: /var/lib/mysql
         volumes:
         - name: mysql-persistent-storage
           persistentVolumeClaim:
             claimName: px-mysql-pvc

Create sharedv4 CSI-enabled volumes

Create sharedv4 CSI-enabled volumes by performing the following steps.

1. Create a sharedv4 PVC by creating the following shared-pvc.yaml file:

   kind: PersistentVolumeClaim
   apiVersion: v1
   metadata:
     name: px-mysql-pvc
   spec:
     storageClassName: px-csi-db
     accessModes:
       - ReadWriteMany
     resources:
       requests:
         storage: 2Gi

2. Apply the shared-pvc.yaml file:

   oc apply -f shared-pvc.yaml

Clone volumes with CSI

You can clone CSI-enabled volumes, duplicating both the volume and content within it.

1. Create a PVC that references the PVC you wish to clone, specifying the dataSource with the kind and name of the target PVC you wish to clone. The following spec creates a clone of the px-mysql-pvc PVC in a YAML file named clonePVC.yaml:

   kind: PersistentVolumeClaim
   apiVersion: v1
   metadata:
       name: clone-of-px-mysql-pvc
   spec:
       storageClassName: px-csi-db
       accessModes:
         - ReadWriteOnce
       resources:
         requests:
           storage: 2Gi
       dataSource:
       kind: PersistentVolumeClaim
       name: px-mysql-pvc

2. Apply the clonePVC.yaml spec to create the clone:

   oc apply -f clonePVC.yaml

Migrate to CSI PVCs

Currently, you cannot migrate or convert PVCs created using the native Kubernetes driver to the CSI driver. However, this is not required, and both types of PVCs can co-exist on the same cluster.