OpenEBS Local Device CSI Driver

CSI Driver for using Local Block Devices

Project Status

Currently, the Device-LocalPV CSI Driver is in alpha. The users/organizations using OpenEBS can be found here

Usage

Prerequisites

Before installing the device CSI driver please make sure your Kubernetes Cluster must meet the following prerequisites:

Disks are available on the node with a single 10MB partition having partition name used to identify the disk
You have access to install RBAC components into kube-system namespace. The OpenEBS Device driver components are installed in kube-system namespace to allow them to be flagged as system critical components.

Supported System

K8S : 1.20+

OS : Ubuntu

Setup

Find the disk which you want to use for the Device LocalPV, for testing a loopback device can be used

truncate -s 1024G /tmp/disk.img
sudo losetup -f /tmp/disk.img --show

MetaPartition

A meta partition is a small (~10MiB) partition that needs to be created on the disk, so as store the disk identification information. In device localpv, the partition name of the meta partition is used to identify the disk. A partition should follow the below criteria, so that openebs identifies it as a meta partition and use it for disk identification

The partition number should be 1 (ID_PART_ENTRY_NUMBER=1)
The partition should not be formatted with any filesystem
The partition should not have any flags set on it

Create the meta partition on the loop device which will be used for provisioning volumes

sudo parted /dev/loop9 mklabel gpt
sudo parted /dev/loop9 mkpart test-device 1MiB 10MiB

Installation

Deploy the Operator yaml

kubectl apply -f https://raw.githubusercontent.com/openebs/device-localpv/develop/deploy/device-operator.yaml

Deployment

1. Create a Storage class

$ cat sc.yaml

apiVersion: storage.k8s.io/v1
kind: StorageClass
metadata:
  name: openebs-device-sc
allowVolumeExpansion: true
parameters:
  devname: "test-device"
provisioner: device.csi.openebs.io
volumeBindingMode: WaitForFirstConsumer

Check the doc on storageclasses to know all the supported parameters for Device LocalPV

Device Availability

If the device with meta partition is available on certain nodes only, then make use of topology to tell the list of nodes where we have the devices available. As shown in the below storage class, we can use allowedTopologies to describe device availability on nodes.

apiVersion: storage.k8s.io/v1
kind: StorageClass
metadata:
  name: openebs-device-sc
allowVolumeExpansion: true
parameters:
  devname: "test-device"
provisioner: device.csi.openebs.io
allowedTopologies:
- matchLabelExpressions:
  - key: kubernetes.io/hostname
    values:
      - device-node1
      - device-node2

The above storage class tells that device with meta partition "test-device" is available on nodes device-node1 and device-node2 only. The Device CSI driver will create volumes on those nodes only.

Scheduler

The OpenEBS Device driver has its own scheduler which will try to distribute the PV across the nodes so that one node should not be loaded with all the volumes. Currently, the driver supports two scheduling algorithms: VolumeWeighted and CapacityWeighted, in which it will try to find a device which has lesser number of volumes provisioned in it or less capacity of volume provisioned out of a device respectively, from all the nodes where the devices are available. To know about how to select scheduler via storage-class See this. Once it is able to find the node, it will create a PV for that node and also create a DeviceVolume custom resource for the volume with the node information. The watcher for this DeviceVolume CR will get all the information for this object and creates a partition with the given size on the mentioned node.

The scheduling algorithm currently only accounts for either the number of volumes or total capacity occupied from a device and does not account for other factors like available cpu or memory while making scheduling decisions. So if you want to use node selector/affinity rules on the application pod, or have cpu/memory constraints, kubernetes scheduler should be used. To make use of kubernetes scheduler, you can set the volumeBindingMode as WaitForFirstConsumer in the storage class. This will cause a delayed binding, i.e kubernetes scheduler will schedule the application pod first, and then it will ask the Device driver to create the PV. The driver will then create the PV on the node where the pod is scheduled.

apiVersion: storage.k8s.io/v1
kind: StorageClass
metadata:
  name: openebs-device-sc
allowVolumeExpansion: true
parameters:
  devname: "test-device"
provisioner: device.csi.openebs.io
volumeBindingMode: WaitForFirstConsumer

Please note that once a PV is created for a node, application using that PV will always get scheduled to that particular node only, as PV will be sticky to that node. The scheduling algorithm by Device driver or kubernetes will come into picture only during the deployment time. Once the PV is created, the application can not move anywhere as the data is there on the node where the PV is.

2. Create the PVC

$ cat pvc.yaml

kind: PersistentVolumeClaim
apiVersion: v1
metadata:
  name: csi-devicepv
spec:
  storageClassName: openebs-device-sc
  accessModes:
    - ReadWriteOnce
  resources:
    requests:
      storage: 4Gi

Create a PVC using the storage class created for the Device driver.

3. Deploy the application

Create the deployment yaml using the pvc backed by Device driver storage.

$ cat fio.yaml

apiVersion: v1
kind: Pod
metadata:
  name: fio
spec:
  restartPolicy: Never
  containers:
  - name: perfrunner
    image: openebs/tests-fio
    command: ["/bin/bash"]
    args: ["-c", "while true ;do sleep 50; done"]
    volumeMounts:
       - mountPath: /datadir
         name: fio-vol
    tty: true
  volumes:
  - name: fio-vol
    persistentVolumeClaim:
      claimName: csi-devicepv

After the deployment of the application, we can go to the node and see that the partition is created and is being used as a volume by the application for reading/writting the data.

4. Deprovisioning

for deprovisioning the volume we can delete the application which is using the volume and then we can go ahead and delete the pv, as part of deletion of pv the partition will be wiped and deleted from the device.

$ kubectl delete -f fio.yaml
pod "fio" deleted
$ kubectl delete -f pvc.yaml
persistentvolumeclaim "csi-devicepv" deleted

openebs-archive/device-localpv