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Using StorageClasses with Pure Service Orchestrator

NOTE THAT THIS ONLY APPLIES TO THE CSI VERSION OF PSO

PSO creates persistent volumes within the federated storage pool of backend appliances defined using criteria defined in the StorageClass used to request the persistent volume.

What is a StorageClass

A StorageClass allow administrators to define various storage configurations to provide high availability, serve quality-of-service requirements, tune file system options, define backup policies, and more. PSO utilizes these storage classes to decide where to provision volumes and how to make the file system.

For more information on StorageClass go here

Provided Storage Classes

As part of the installation of PSO, three storage classes are created which can be used to simply create persistent volumes on a file or a block backend device within the federated storage pool using all the default settings PSO has provided.

Two of these are called pure-file and pure-block and, as their names suggest, they will create persistent volumes from the block providing or file providing backends within the federated pool of backend devices. At all times the load-balancing algorithm within PSO will ensure that the persistent volume is created on the most appropriate backend given the block or file requirement, even if there are multiple block or file providing appliances in the pool.

The third StorageClass is simply called pure. This is provided primarily as a legacy class to provide backwards capability with early PSO releases. By default this storage class uses block storage appliances to provision block-based persistent volumes, however, this can be modified in the PSO configuration values.yaml.

Default StorageClass

Within the PSO configuration file is a setting to enable the pure StorageClass as the default class for the Kubernetes cluster. To enable pure as the default class set the following parameter in values.yaml

  storageClass:
    isPureDefault: true

As mentioned above, the pure class uses block-based backend appliances to provision persistent volumes from. It is possible to change this default setting to use file-backed appliances from the pool.

You may wish to do this if you only have FlashBlades in your PSO configuration, as these can only provide file-based persistent volumes.

To change the backend type used by the pure StorageClass to file rather than block, change the following line within the values.yaml configuration file:

  pureBackend: file

Creating your own Storage Classes for PSO to use

With the increasing options available to configure the persistent volumes supported by PSO it may be necessary to create additional storage classes that will use PSO to provide specific configurations of persistent volume.

For example, if you wish to provide raw block volumes (shortly to be supported by PSO) then you will need to request these from a StorageClass that knows how to do this. Alternatively, you may have a requirement for some block-based persistent volumes to be formatted with the btfs file system rather than the default xfs file system provided by PSO through the pure-block StorageClass, or the default Kubernetes filesystem of ext4

[NOTE: Pure does not recommend using ext4 as a filesystem for persistent volumes in containers]

With the addition of per volume filesystem options, the ability to use a different StorageClass for different requirements becomes critical.

To create a storageClass that will use PSO use the following template and modify as required for your custom storage class.

  kind: StorageClass
  apiVersion: storage.k8s.io/v1
  metadata:
    name: <your storageClass name>
    labels:
      kubernetes.io/cluster-service: "true"
  provisioner: pure-csi
  parameters:

Within the parameters section is where you add your own custom settings. More details of some of the options available to use in the parameters section can be found here

Once you have created your StorageClass definition in a YAML file, create it in Kubernetes using the command

kubectl apply -f <storageclassdefinition>.yaml

If you wish to ensure your new StoraegClass is the default class then add the following into the metadata section of the definition:

  annotations:
    storageclass.kubernetes.io/is-default-class: true

NOTE: if a StorageClass is already flagged as default your new StorageClass will not take its place, but you will have multiple default storage classes. In this case Kubernetes will completely ignore the default flags and you may fail to create the persistent volumes you expected.