Create and use storage classes in VM Runtime on GDC

This document is intended for application owners and platform administrators that run Google Distributed Cloud. This document shows you how to create and use storage classes for VMs that use VM Runtime on GDC. A StorageClass lets you define different storage configurations to provide for the various needs of your VMs.

Before you begin

To complete this document, you need access to Google Distributed Cloud version 1.12.0 (anthosBareMetalVersion: 1.12.0) or higher cluster. You can use any cluster type capable of running workloads. If needed, try Google Distributed Cloud on Compute Engine or see the cluster creation overview.

Storage classes overview

You use a StorageClass to define the type of storage you make available to VMs. Different storage classes might map to a different type of storage hardware, file system, or performance. You can create and use storage classes to support your compute workloads in VM Runtime on GDC. For more information, see Storage Classes.

A default StorageClass can be defined in the custom resource for VM Runtime on GDC. If you don't define a specific class when you create a VirtualMachineDisks, this default StorageClass is used. No initial StorageClass is configured and set as default. In the following section, you learn how to set or update this default StorageClass.

Set or update the default StorageClass

Initially, Google Distributed Cloud with VM Runtime on GDC have no default StorageClass configured. To create a VirtualMachineDisk without specifying a StorageClass, you must first create a StorageClass and then set it as default.

If you want to initially set or update the default StorageClass that VM Runtime on GDC uses when you create a VirtualMachineDisk, update the VMRuntime custom resource.

Edit the VMRuntime custom resource:
```
kubectl edit vmruntime
```
Add or update the spec.storage section that specifies the default StorageClass to use:
```
apiVersion: vm.cluster.gke.io/v1
kind: VMRuntime
metadata:
  name: vmruntime
spec:
  enabled: true
  storage:
    defaultStorageClass: STORAGE_CLASS_NAME
...
```
Edit STORAGE_CLASS_NAME with the name of the default StorageClass you want to use. If you need to first create a StorageClass, see Create a StorageClass.
Save and close the VMRuntime custom resource in your editor.

The StorageClass you specified is now used when you now create a virtual machine disk and don't specify a StorageClass. The following section shows you how to create a disk and use a specific StorageClass.

Existing VirtualMachineDisk resources are not updated to use the newly specified StorageClass.

Use a specific StorageClass

If you don't want to use the default StorageClass when you create a VirtualMachineDisk, use the storageClassName field to specify a different StorageClass.

To use a specific, already-defined StorageClass when you create a VirtualMachineDisk, complete the following steps:

Create a VirtualMachineDisk manifest, such as my-disk.yaml, in the editor of your choice:
```
nano my-disk.yaml
```
Copy and paste the following YAML manifest:
```
apiVersion: vm.cluster.gke.io/v1
kind: VirtualMachineDisk
metadata:
  name: DISK_NAME
spec:
  size: 10Gi
  storageClassName: STORAGE_CLASS_NAME
```
Replace the following values:
- DISK_NAME: the name for your disk.
- STORAGE_CLASS_NAME: the StorageClass to use for your disk. This StorageClass must already exist. If you need to first create a StorageClass, see Create a StorageClass.
Save and close the disk manifest in your editor.
Create the disk using kubectl:
```
kubectl apply -f my-disk.yaml
```

Configure storage profiles

Storage profiles provide extra configuration options associated with each StorageClass. These configuration options include which access mode and volume mode to use for VirtualMachineDisks that use the StorageClass.

Without a configured storage profile, disks default to the ReadWriteOnce access mode. This access mode isn't sufficient for production workloads, as features like live migration don't work. The default volume mode without a configured storage profile is Filesystem.

VM Runtime on GDC automatically generates one storage profile for each StorageClass in a cluster. The storage profile is the same name as the associated StorageClass. The following example output shows that the cluster has four storage classes and associated profiles:

  $ kubectl get storageprofiles

  NAME            AGE
  anthos-system   11d
  node-disk       11d
  standard        11d
  nfs             11d

To edit a storage profile and change the access mode or volume mode, complete the following steps:

Edit the StorageProfile custom resource for editing:
```
kubectl edit storageprofile STORAGE_PROFILE_NAME
```
Replace STORAGE_PROFILE_NAME with the StorageProfile you want to edit.
Add a single entry to the spec.claimPropertySets list of the StorageProfile:
```
apiVersion: cdi.kubevirt.io/v1beta1
kind: StorageProfile
metadata:
  name: nfs
spec:
  claimPropertySets:
  - accessModes:
    - ACCESS_MODE
    volumeMode: VOLUME_MODE
```
The accessMode and volumeMode use the underlying Kubernetes components. The values you set depend on the storage driver you use. Replace the following values as appropriate for the storage you use:
- ACCESS_MODE: the access mode that you want to use. If supported by the associated StorageClass, the preferred access mode is ReadWriteMany.
  - Acceptable values include ReadWriteOnce, ReadOnlyMany, ReadWriteMany, and ReadWriteOncePod. If not specified, ReadWriteOnce is used based on the VM Runtime on GDC defaults. For more information, see Access modes.
- VOLUME_MODE: the volume mode that you want to use.
  - Acceptable values include Filesystem and Block. If not specified, Filesystem is used based on the Kubernetes defaults. For more information, see Volume modes.
Note: The access mode and volume mode must be supported by the underlying StorageClass.
Save and close the StorageProfile custom resource in your editor.

The storage profile settings you defined are used when you now create any virtual disks. Existing VirtualMachineDisk resources are not updated to use the defined storage profile settings.