drbdadm

drbdadm is a command-line administration tool for managing DRBD (Distributed Replicated Block Device) resources. It was widely used with earlier versions of DRBD (such as DRBD8) to control replication, manage device states, and coordinate configuration settings as defined in /etc/drbd.conf and the /etc/drbd.d/ directory. In more recent versions of DRBD (version 9 and later), drbdsetup has largely replaced drbdadm for many tasks, but drbdadm remains relevant for legacy systems.

Purpose

• Resource Management: drbdadm is used to bring DRBD devices up or down, promote them to primary status, or demote them to secondary. This is essential in managing which node is actively serving data and which is in standby for replication.

• Configuration Coordination: It reads DRBD configurations from global and resource-specific files, ensuring that devices are initialized and managed according to defined parameters.

• Operational Control: Provides commands to check the current status of DRBD devices, verify synchronization states, and adjust runtime parameters when necessary.

Key Commands and Operations

drbdadm supports several key commands that operate on a given DRBD resource (typically identified by its resource name, as defined in your configuration):

• up: Activates a DRBD resource, starting the replication process.

  drbdadm up <resource>

  Example:

  drbdadm up r0

• down: Deactivates a DRBD resource, stopping replication and detaching the DRBD device.

  drbdadm down <resource>

  Example:

  drbdadm down r0

• primary/secondary: Manages the role of a DRBD device.

  • primary: Promotes the resource to primary, enabling read/write access.

    drbdadm primary <resource>

  • secondary: Demotes the resource to secondary.

    drbdadm secondary <resource>

• status: Displays the current status of DRBD resources, including connection state, synchronization progress, and role (primary/secondary).

  drbdadm status <resource>

• verify: Verifies the consistency and health of DRBD metadata or the replication status.

  drbdadm verify <resource>

Additional commands may exist for advanced operations or for interacting with DRBD metadata.

Example Workflow

1. Bring a Resource Online:

   drbdadm up r0

   This command initializes the DRBD resource r0 based on its configuration.

2. Promote the Resource to Primary:

   drbdadm primary r0

   With this command, the resource r0 is promoted to primary status, allowing it to handle read/write operations.

3. Check the Status of the Resource:

   drbdadm status r0

   This command shows the current state of r0, including its role, connection state, and synchronization details.

4. Take the Resource Down for Maintenance:

   drbdadm down r0

   This stops the DRBD service for resource r0 safely, which is useful during maintenance or configuration changes.

Transition to drbdsetup

While drbdadm has been the traditional tool for DRBD management, in DRBD version 9 and newer, drbdsetup is now recommended for most administrative tasks. drbdsetup offers a modernized and unified interface that consolidates several functions, making it more straightforward to manage DRBD devices. However, understanding drbdadm remains important when working with legacy systems or when maintaining older configurations.

Conclusion

drbdadm is a critical administration tool for managing DRBD resources in older DRBD implementations. It enables system administrators to control the lifecycle of DRBD devices through operations such as bringing devices up or down, promoting/demoting their roles, and checking their status. Although its functionality has been largely superseded by drbdsetup in modern DRBD versions, drbdadm continues to be an essential tool in environments that run legacy DRBD systems.