CSI automatic migration - Using Container Storage Interface (CSI) | Storage

Overview
Automatic migration of in-tree volumes to CSI
Manually enabling CSI automatic migration

In-tree storage drivers that are traditionally shipped with OpenShift Container Platform are being deprecated and replaced by their equivalent Container Storage Interface (CSI) drivers. OpenShift Container Platform provides automatic migration for certain supported in-tree volume plugins to their equivalent CSI drivers.

Overview

Volumes that are provisioned by using in-tree storage plugins, and that are supported by this feature, are migrated to their counterpart Container Storage Interface (CSI) drivers. This process does not perform any data migration; OpenShift Container Platform only translates the persistent volume object in memory. As a result, the translated persistent volume object is not stored on disk, nor is its contents changed.

The following in-tree to CSI drivers are supported:

Table 1. CSI automatic migration feature supported in-tree/CSI drivers
In-tree/CSI drivers	Support level	CSI auto migration enabled automatically?
Azure Disk OpenStack Cinder	Generally available (GA)	Yes. For more information, see "Automatic migration of in-tree volumes to CSI".
Amazon Web Services (AWS) Elastic Block Storage (EBS) Azure File Google Compute Engine Persistent Disk (in-tree) and Google Cloud Platform Persistent Disk (CSI) VMware vSphere	Technology Preview (TP)	No. To enable, see "Manually enabling CSI automatic migration".

CSI automatic migration should be seamless. This feature does not change how you use all existing API objects: for example, PersistentVolumes, PersistentVolumeClaims, and StorageClasses.

Enabling CSI automatic migration for in-tree persistent volumes (PVs) or persistent volume claims (PVCs) does not enable any new CSI driver features, such as snapshots or expansion, if the original in-tree storage plugin did not support it.

Additional resources

Automatic migration of in-tree volumes to CSI

OpenShift Container Platform supports automatic and seamless migration for the following in-tree volume types to their Container Storage Interface (CSI) driver counterpart:

Azure Disk
OpenStack Cinder

CSI migration for these volume types is considered generally available (GA), and requires no manual intervention.

For new OpenShift Container Platform 4.11, and later, installations, the default storage class is the CSI storage class. All volumes provisioned using this storage class are CSI persistent volumes (PVs).

For clusters upgraded from 4.10, and earlier, to 4.11, and later, the CSI storage class is created, and is set as the default if no default storage class was set prior to the upgrade. In the very unlikely case that there is a storage class with the same name, the existing storage class remains unchanged. Any existing in-tree storage classes remain, and might be necessary for certain features, such as volume expansion to work for existing in-tree PVs. While storage class referencing to the in-tree storage plugin will continue working, we recommend that you switch the default storage class to the CSI storage class.

Manually enabling CSI automatic migration

If you want to test Container Storage Interface (CSI) migration in development or staging OpenShift Container Platform clusters, you must manually enable in-tree to CSI migration for the following in-tree volume types:

AWS Elastic Block Storage (EBS)
Google Compute Engine Persistent Disk (GCE-PD)
VMware vSphere Disk
Azure File

CSI automatic migration for the preceding in-tree volume plugins and CSI driver pairs is a Technology Preview feature only. Technology Preview features are not supported with Red Hat production service level agreements (SLAs) and might not be functionally complete. Red Hat does not recommend using them in production. These features provide early access to upcoming product features, enabling customers to test functionality and provide feedback during the development process.

For more information about the support scope of Red Hat Technology Preview features, see Technology Preview Features Support Scope.

After migration, the default storage class remains the in-tree storage class.

CSI automatic migration will be enabled by default for all storage in-tree plugins in a future OpenShift Container Platform release, so it is highly recommended that you test it now and report any issues.

Enabling CSI automatic migration drains, and then restarts, all nodes in the cluster in sequence. This might take some time.

Procedure

Enable feature gates (see Nodes → Working with clusters → Enabling features using feature gates).

After turning on Technology Preview features using feature gates, they cannot be turned off. As a result, cluster upgrades are prevented.

The following configuration example enables CSI automatic migration for all CSI drivers supported by this feature that are currently in Technology Preview (TP) status:
```
apiVersion: config.openshift.io/v1
kind: FeatureGate
metadata:
  name: cluster
spec:
  featureSet: TechPreviewNoUpgrade (1)
...
```
1 Enables automatic migration for AWS EBS, GCP, Azure File, and VMware vSphere.

You can specify CSI automatic migration for a selected CSI driver by setting CustomNoUpgrade featureSet and for featuregates to one of the following:
- CSIMigrationAWS
- CSIMigrationAzureFile
- CSIMigrationGCE
- CSIMigrationvSphere
The following configuration example enables automatic migration to the AWS EBS CSI driver only:
```
apiVersion: config.openshift.io/v1
kind: FeatureGate
metadata:
  name: cluster
spec:
  featureSet: CustomNoUpgrade
  customNoUpgrade:
    enabled:
      - CSIMigrationAWS (1)
    ...
```
1 Enables automatic migration for AWS EBS only.

Additional resources

Enabling features using feature gates