Azure Disk CSI Driver Operator - Using Container Storage Interface (CSI) | Storage

Overview
About CSI
Machine sets that deploy machines with ultra disks using PVCs
- Creating machines with ultra disks by using machine sets
- Troubleshooting resources for machine sets that enable ultra disks
Additional resources

Overview

OKD 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, OKD 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 OKD users storage options, such as volume snapshots, that are not possible with in-tree volume plug-ins.

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

In future OKD 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 OKD.

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.

Additional resources

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

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.

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.

Create a machine set using the updated configuration by running the following command:
```
$ oc create -f <machine-set-name>.yaml
```

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.

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`.

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

Validate that the machines are created by running the following command:
```
$ oc get machines
```
The machines should be in the Running state.
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>
```