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drdb

Introduction​

This cheat sheet provides a quick reference for some common drbd (Distributed Replicated Block Device) commands and concepts. drbd is a Linux kernel module and userspace utility used for replicating and mirroring block devices between multiple nodes in a cluster.

drbd Concepts​

Resources​

drbd manages data replication through resources, which represent block devices to be replicated.

  • Define a new drbd resource:
    resource r0 {
      device minor;
      disk disk;
      meta-disk disk;
      on node;
      address IP:port;
    }

Connection States​

drbd uses connection states to represent the status of replication between nodes.

  • WFConnection: Waiting for connection.
  • WFReportParams: Waiting for report parameters.
  • WFBitMapS: Waiting for bitmap synchronization.
  • Established: Replication established.

Resource States​

Resources have various states indicating their status.

  • Unconfigured: Resource is not configured.
  • UpToDate: Data is up-to-date.
  • Outdated: Data is outdated and needs synchronization.
  • Diskless: Resource has no local storage.

Synchronization​

Synchronization is the process of ensuring data consistency between nodes.

  • Start initial synchronization:

    drbdadm -- --overwrite-data-of-peer primary <resource>

  • View synchronization progress:

    cat /proc/drbd

Failover​

Failover is the process of switching from one node to another in case of a failure.

  • Promote a resource to primary on a node:

    drbdadm primary <resource>

  • Promote a resource to primary and disconnect it from another node:

    drbdadm disconnect <resource>

drbd Command-Line​

  • Start the drbd service on a node:

    systemctl start drbd

  • Stop the drbd service on a node:

    systemctl stop drbd

  • View the status of drbd resources:

    drbdadm status

  • Show detailed information about a drbd resource:

    drbdadm dstate <resource>

Conclusion​

This cheat sheet covers some common drbd (Distributed Replicated Block Device) commands and concepts. drbd is a powerful tool for replicating and mirroring block devices in a cluster, ensuring high availability and data redundancy; refer to the official drbd documentation for more in-depth information and advanced usage.