Raw Block Devices

Summary and Key concepts

Summary:

This article explains how to use Portworx CSI Driver for creating and managing raw block devices in Kubernetes or OpenShift environments. It highlights support for both file and block volume types and describes how to create a PersistentVolumeClaim (PVC) with block volume mode for applications that require raw block devices. The article walks through creating a PersistentVolumeClaim and deployment YAML configurations for using raw block storage with a Kubernetes deployment. Specific instructions for applying these configurations differ slightly based on the environment, whether using kubectl or oc for OpenShift.

Kubernetes Concepts:

• PersistentVolumeClaim (PVC): A request for storage by a user.
• VolumeMode: By setting a Block mode in PVCs allows raw block devices to be requested instead of file-based volumes.
• StorageClass: Defines the class of storage to be used for PVCs.
• Deployment: A Kubernetes object that manages a replicated application, updating and scaling based on specifications.
• VolumeDevices: Used to mount raw block devices inside containers.

Portworx Concepts:

• Portworx CSI Driver: Implements the CSI specification to expose Portworx storage as file or block volumes in Kubernetes.
• CSI Enabled Storage Classes: Preconfigured storage classes for CSI in Portworx.

The Portworx CSI Driver supports both File and Block volume types in Kubernetes PVCs. While file has more supported features, block support for ReadWriteOnly PVCs was added in Portworx Enterprise in version 2.8.0.

Use cases for Raw Block Devices

If your application has a requirement to consume a raw block device as opposed to a mounted filesystem, this is a perfect use case for Portworx CSI Raw Block devices.

note

Currently, only ReadWriteOnce PVCs can be created with the block volume mode.

Create and use raw block PVCs

In this example we are using the px-csi-db storage class out of the box. Please refer CSI Enabled Storage Classes for list of available CSI enabled storage classes offered by Portworx.

1. Create a PVC spec that references the portworx-csi-sc as seen below in a YAML file named raw-block-pvc.yaml:

   kind: PersistentVolumeClaim
   apiVersion: v1
   metadata:
      name: px-csi-raw-block-pvc
   spec:
      volumeMode: Block
      storageClassName: px-csi-db
      accessModes:
        - ReadWriteOnce
      resources:
        requests:
          storage: 2Gi

2. Apply the raw-block-pvc.yaml spec to create the raw block PVC:

   kubectl apply -f raw-block-pvc.yaml

3. Create a deployment SPEC that references the above raw block PVC in raw-block-deployment.yaml:

   apiVersion: apps/v1
   kind: Deployment
   metadata:
     name: ioping
   spec:
     selector:
       matchLabels:
         app: ioping
     strategy:
       rollingUpdate:
         maxSurge: 1
         maxUnavailable: 1
       type: RollingUpdate
     replicas: 1
     template:
       metadata:
         labels:
           app: ioping
           version: "1"
       spec:
         containers:
         - name: ioping 
           image: hpestorage/ioping 
           command: [ "ioping" ] 
           args: [ "/dev/xvda" ] 
           volumeDevices: 
           - name: raw-device 
             devicePath: /dev/xvda 
         volumes:
         - name: raw-device
           persistentVolumeClaim:
             claimName: px-csi-raw-block-pvc

4. Apply the raw-block-deployment.yaml spec to create the deployment utilizing our raw block PVC:

   kubectl apply -f raw-block-deployment.yaml