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Overview

OpenShift Container Platform is capable of provisioning persistent volumes (PVs) using the Container Storage Interface (CSI) driver for Microsoft Azure Disk Storage.

Familiarity with persistent storage and configuring CSI volumes is recommended when working with a CSI Operator and driver.

To create CSI-provisioned PVs that mount to Azure Disk storage assets, OpenShift Container Platform installs the Azure Disk CSI Driver Operator and the Azure Disk CSI driver by default in the openshift-cluster-csi-drivers namespace.

  • The Azure Disk CSI Driver Operator provides a storage class named managed-csi that you can use to create persistent volume claims (PVCs). The Azure Disk CSI Driver Operator supports dynamic volume provisioning by allowing storage volumes to be created on-demand, eliminating the need for cluster administrators to pre-provision storage.

  • The Azure Disk CSI driver enables you to create and mount Azure Disk PVs.

About CSI

Storage vendors have traditionally provided storage drivers as part of Kubernetes. With the implementation of the Container Storage Interface (CSI), third-party providers can instead deliver storage plug-ins using a standard interface without ever having to change the core Kubernetes code.

CSI Operators give OpenShift Container Platform users storage options, such as volume snapshots, that are not possible with in-tree volume plug-ins.

OpenShift Container Platform defaults to using an in-tree (non-CSI) plug-in to provision Azure Disk storage.

In future OpenShift Container Platform versions, volumes provisioned using existing in-tree plug-ins are planned for migration to their equivalent CSI driver. CSI automatic migration should be seamless. Migration does not change how you use all existing API objects, such as persistent volumes, persistent volume claims, and storage classes. For more information about migration, see CSI automatic migration.

After full migration, in-tree plug-ins will eventually be removed in later versions of OpenShift Container Platform.

Machine sets that deploy machines with ultra disks using PVCs

You can create a machine set running on Azure that deploys machines with ultra disks. Ultra disks are high-performance storage that are intended for use with the most demanding data workloads.

Both the in-tree plug-in and CSI driver support using PVCs to enable ultra disks. You can also deploy machines with ultra disks as data disks without creating a PVC.

Creating machines with ultra disks by using machine sets

You can deploy machines with ultra disks on Azure by editing your machine set YAML file.

Prerequisites
  • Have an existing Microsoft Azure cluster.

Procedure
  1. Copy an existing Azure MachineSet custom resource (CR) and edit it by running the following command:

    $ oc edit machineset <machine-set-name>

    where <machine-set-name> is the machine set that you want to provision machines with ultra disks.

  2. Add the following lines in the positions indicated:

    apiVersion: machine.openshift.io/v1beta1
    kind: MachineSet
      ...
    spec:
      ...
      template:
        ...
        spec:
          metadata:
            ...
            labels:
              ...
              disk: ultrassd (1)
              ...
          providerSpec:
            value:
              ...
              ultraSSDCapability: Enabled (2)
                 ...
    1 Specify a label to use to select a node that is created by this machine set. This procedure uses disk.ultrassd for this value.
    2 These lines enable the use of ultra disks.
  3. Create a machine set using the updated configuration by running the following command:

    $ oc create -f <machine-set-name>.yaml
  4. Create a storage class that contains the following YAML definition:

    apiVersion: storage.k8s.io/v1
    kind: StorageClass
    metadata:
      name: ultra-disk-sc (1)
    parameters:
      cachingMode: None
      diskIopsReadWrite: "2000" (2)
      diskMbpsReadWrite: "320" (3)
      kind: managed
      skuname: UltraSSD_LRS
    provisioner: disk.csi.azure.com (4)
    reclaimPolicy: Delete
    volumeBindingMode: WaitForFirstConsumer (5)
    1 Specify the name of the storage class. This procedure uses ultra-disk-sc for this value.
    2 Specify the number of IOPS for the storage class.
    3 Specify the throughput in MBps for the storage class.
    4 For Azure Kubernetes Service (AKS) version 1.21 or later, use disk.csi.azure.com. For earlier versions of AKS, use kubernetes.io/azure-disk.
    5 Optional: Specify this parameter to wait for the creation of the pod that will use the disk.
  5. Create a persistent volume claim (PVC) to reference the ultra-disk-sc storage class that contains the following YAML definition:

    apiVersion: v1
    kind: PersistentVolumeClaim
    metadata:
      name: ultra-disk (1)
    spec:
      accessModes:
      - ReadWriteOnce
      storageClassName: ultra-disk-sc (2)
      resources:
        requests:
          storage: 4Gi (3)
    1 Specify the name of the PVC. This procedure uses ultra-disk for this value.
    2 This PVC references the ultra-disk-sc storage class.
    3 Specify the size for the storage class. The minimum value is 4Gi.
  6. Create a pod that contains the following YAML definition:

    apiVersion: v1
    kind: Pod
    metadata:
      name: nginx-ultra
    spec:
      nodeSelector:
        disk: ultrassd (1)
      containers:
      - name: nginx-ultra
        image: alpine:latest
        command:
          - "sleep"
          - "infinity"
        volumeMounts:
        - mountPath: "/mnt/azure"
          name: volume
      volumes:
        - name: volume
          persistentVolumeClaim:
            claimName: ultra-disk (2)
    1 Specify the label of the machine set that enables the use of ultra disks. This procedure uses disk.ultrassd for this value.
    2 This pod references the ultra-disk PVC.
Verification
  1. Validate that the machines are created by running the following command:

    $ oc get machines

    The machines should be in the Running state.

  2. For a machine that is running and has a node attached, validate the partition by running the following command:

    $ oc debug node/<node-name> -- chroot /host lsblk

    In this command, oc debug node/<node-name> starts a debugging shell on the node <node-name> and passes a command with --. The passed command chroot /host provides access to the underlying host OS binaries, and lsblk shows the block devices that are attached to the host OS machine.

Next steps
  • To use an ultra disk from within a pod, create workload that uses the mount point. Create a YAML file similar to the following example:

    apiVersion: v1
    kind: Pod
    metadata:
      name: ssd-benchmark1
    spec:
      containers:
      - name: ssd-benchmark1
        image: nginx
        ports:
          - containerPort: 80
            name: "http-server"
        volumeMounts:
        - name: lun0p1
          mountPath: "/tmp"
      volumes:
        - name: lun0p1
          hostPath:
            path: /var/lib/lun0p1
            type: DirectoryOrCreate
      nodeSelector:
        disktype: ultrassd

Troubleshooting resources for machine sets that enable ultra disks

Use the information in this section to understand and recover from issues you might encounter.

Unable to mount a persistent volume claim backed by an ultra disk

If there is an issue mounting a persistent volume claim backed by an ultra disk, the pod becomes stuck in the ContainerCreating state and an alert is triggered.

For example, if the additionalCapabilities.ultraSSDEnabled parameter is not set on the machine that backs the node that hosts the pod, the following error message appears:

StorageAccountType UltraSSD_LRS can be used only when additionalCapabilities.ultraSSDEnabled is set.
  • To resolve this issue, describe the pod by running the following command:

    $ oc -n <stuck_pod_namespace> describe pod <stuck_pod_name>