OpenEBS Local PV

Overview

OpenEBS provides Dynamic PV provisioners for Kubernetes Local Volumes. A local volume implies that storage is available only from a single node. A local volume represents a mounted local storage device such as a disk, partition or directory.

As the Local Volume is accessible only from a single node, local volumes are subject to the availability of the underlying node and are not suitable for all applications. If a node becomes unhealthy, then the local volume will also become inaccessible, and a Pod using it will not be able to run. Applications using local volumes must be able to tolerate this reduced availability, as well as potential data loss, depending on the durability characteristics of the underlying disk.

Use Cases

Examples of good workloads that can benefit from local volumes are:

  • Replicated databases like MongoDB, Cassandra
  • Stateful workloads that can be configured with their own high-availability configuration like Elastic, MinIO
  • Edge workloads that typically run on a single node or in Single node Kubernetes Clusters.

OpenEBS helps users to take local volumes into production by providing features that are currently missing in Kubernetes like:

  • Dynamic PV Provisioners for local volumes.
  • Local Volumes backed by hostpath on filesystems like Ext3, XFS or ZFS.
  • Monitoring the health of underlying devices or storage used to create Local Volumes.
  • Capacity management features like over-provisioning and/or quota enforcement.
  • Make use of the underlying storage capabilities like snapshot, clone, compression and so forth when local volumes are backed by advanced filesystem like ZFS.
  • Backup and Restore via Velero.
  • Secure the local volumes via LUKS or by using in-build encryption support of the underlying filesystem like ZFS.

Quick Start Guides

OpenEBS provides different types of Local Volumes that can be used to provide locally mounted storage to Kubernetes Stateful workloads. Follow these guides to get started with each type of Local Volume.

When to use OpenEBS Local PVs

  • High performance is needed by those applications which manage their own replication, data protection and other features such as snapshots and clones.
  • When local disks need to be managed dynamically and monitored for impending notice of them going bad.

When not to use OpenEBS Local PVs

  • When applications expect replication from storage.
  • When the volume size may need to be changed dynamically but the underlying disk is not resizable.

Backup and Restore

OpenEBS Local Volumes can be backed up and restored along with the application using Velero.

Velero uses Restic for backing up and restoring Kubernetes local volumes. Velero can be configured to save the backups either in the cloud or on-premise with any S3 compatible storage like Minio. When user initiates the backup, Velero via the Restic, will copy the entire data from the Local PV to the remote location. Later, when the user wants to restore the application, velero injects an init container into the application that will download and populate the data into the volume from the backed up location. For more details on how Velero Restic works, please see documentation on Velero Restic integration.

While the preferred way for Backup and Restore for cloud native applications using Local Volumes is to use the application specific backup solution, you can use the Velero based Backup and Restore in the following cases:

  • Application doesn’t natively provide a Backup and Restore solution
  • Schedule a Daily or weekly backups of the data during a off-peak hours
  • Migrating the application using Local Volumes to a new Cluster.

You can refer to the Local PV user guides for detailed instructions on Backup and Restore.

A quick summary of the steps to backup include:

  1. Install and Setup Velero by following the Velero Documentation.

  2. Prepare the application that needs to be backed up. Label and annotate the application, indicating that you would like to use velero to backup the volumes. For example, if you would like to backup an application pod named hello-local-hostpath-pod with a volume mount local-storage, you would need to run the following commands.

    1. kubectl label pod hello-local-hostpath-pod app=test-velero-backup
    2. kubectl annotate pod hello-local-hostpath-pod backup.velero.io/backup-volumes=local-storage

  3. Use velero to backup the application.

    1. velero backup create bbb-01 -l app=test-velero-backup

A quick summary of the steps to restore include:

  1. Install and Setup Velero, with the same provider where backups were saved.

  2. Local PVs are created with node affinity. As the node names will change when a new cluster is created, create the required PVC(s) prior to proceeding with restore.

    1. kubectl apply -f https://openebs.github.io/charts/examples/local-hostpath/local-hostpath-pvc.yaml

  3. Use velero to restore the application and populate the data into the volume from the backup.

    1. velero restore create rbb-01 --from-backup bbb-01 -l app=test-velero-backup

Limitations (or Roadmap items ) of OpenEBS Local PVs

  • Size of the Local PV cannot be increased dynamically. LVM type of functionality inside Local PVs is a potential feature in roadmap.
  • Disk quotas are not enforced by Local PV. An underlying device or hostpath can have more data than requested by a PVC or storage class. Enforcing the capacity is a roadmap feature.
  • Enforce capacity and PVC resource quotas on the local disks or host paths.
  • SMART statistics of the managed disks is also a potential feature in roadmap.

See Also:

OpenEBS Architecture

Understanding NDM

Local PV Hostpath User Guide

Local PV Device User Guide

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