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Longhorn Storage Solution

DCE 5.0 supports many third-party storage solutions. We have conducted detailed tests on Longhorn and finally integrated it into the app store as an Addon. The following is a brief research and evaluation report on Longhorn.

Longhorn is a lightweight cloud native Kubernetes distributed storage platform that can run on any infrastructure. Longhorn and DCE can be used together to deploy high-availability persistent block storage.

  1. Design and Architecture

    • Control Plane: Longhorn Manager deployed with DaemonSet.
    • Data Plane: Longhorn Engine is a storage controller that can have multiple replicas.

  2. Longhorn Storage Volumes

    • Supports thin provisioning of storage volumes.
    • Storage volume maintenance mode is used for snapshot reverting operations.
    • Each volume replica contains multiple snapshots.
    • The default number of replicas for a storage volume can be set in the settings. The number of replicas can be changed through the UI after the storage volume is mounted.
    • Longhorn is a crash-consistent block storage solution that automatically synchronizes the sync command before creating a snapshot.

  3. Data Backup and External Secondary Storage

    • NFS/S3-compatible external secondary storage for backups is independent of the Kubernetes cluster. Data remains available even if the Kubernetes cluster is unavailable.
    • Longhorn will also synchronize the storage volume to the secondary storage of the disaster recovery (DR) cluster for disaster data recovery.
    • A backup is a flattened collection of multiple snapshot data.
    • Supports continuous and repeated snapshots and backups.
    • Supports cloning of CSI storage volumes.

  4. High Availability

    • Supports replica automatic balance setting.
    • Supports data locality setting: there is at least one replica copy on the node running the pod using the storage volume.
    • Supports displaying node storage space usage.
    • Supports Kubernetes Cluster Autoscaler (Experimental).
    • Supports automatic recovery after storage volumes are accidentally unmounted.
    • Supports automatic recovery of storage volumes after cluster node failure.

  5. Monitoring

    • Supports Prometheus and Grafana to monitor Longhorn.
    • Longhorn metrics can be integrated into the DCE monitoring system.
    • Supports kubelet metrics monitoring.
    • Supports Longhorn alert strategy.

  6. Advanced Features

    • Supports backing images.
    • Supports orphaned replica directories.
    • Supports DCE cluster recovery: recovery of all storage volumes in the cluster.
    • Supports multiple write operations for ReadWriteMany (RWX) workloads (NFSv4).
    • Supports using Longhorn Volume as an iSCSI target.

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