Ceph MON_QUORUM_LOST

What is Ceph MON_QUORUM_LOST

Understanding Ceph and Its Purpose

Ceph is an open-source software-defined storage platform that provides highly scalable object, block, and file-based storage under a unified system. It is designed to be self-healing and self-managing, minimizing administration time and other costs. Ceph's architecture is based on the Reliable Autonomic Distributed Object Store (RADOS), which ensures data redundancy and reliability.

Recognizing the Symptom: MON_QUORUM_LOST

When working with Ceph, you might encounter the error MON_QUORUM_LOST. This error indicates that the monitor quorum is lost. The monitor quorum is crucial for maintaining the consistency and availability of the Ceph cluster. When this error occurs, you might observe that the cluster becomes read-only or unresponsive.

Explaining the Issue: Monitor Quorum Lost

The MON_QUORUM_LOST error typically arises due to network partitions or the failure of multiple monitor daemons. In a Ceph cluster, monitors (MONs) are responsible for maintaining the cluster map and state. A quorum is achieved when a majority of the monitors are in agreement about the cluster state. If the quorum is lost, the cluster cannot function properly.

Common Causes

Network issues causing partitions between monitor nodes. Multiple monitor daemons failing simultaneously. Insufficient number of monitors to maintain a quorum.

Steps to Resolve MON_QUORUM_LOST

To resolve the MON_QUORUM_LOST error, follow these steps:

Step 1: Check Network Connectivity

Ensure that all monitor nodes can communicate with each other. Use the following command to test connectivity:

ping <monitor-node-ip>

If there are connectivity issues, resolve them by checking network configurations, firewalls, or any other network-related settings.

Step 2: Restart Monitor Daemons

If any monitor daemons have failed, restart them using the following command:

systemctl restart ceph-mon@<mon-id>

Replace <mon-id> with the appropriate monitor identifier.

Step 3: Verify Monitor Status

Check the status of the monitors to ensure they are running correctly:

ceph mon stat

This command will provide information about the current state of the monitor nodes.

Step 4: Consider Adding More Monitors

If your cluster frequently loses quorum, consider adding more monitors to increase redundancy. Follow the official Ceph documentation on adding or removing monitors.

Conclusion

Maintaining a healthy monitor quorum is essential for the stability and performance of a Ceph cluster. By ensuring network connectivity, restarting failed daemons, and potentially adding more monitors, you can resolve the MON_QUORUM_LOST error and keep your cluster running smoothly.

For more detailed information, refer to the Ceph Documentation.