Ceph MDS failover is not occurring as expected.

Configuration issues with MDS or improperly configured standby MDS instances.

Understanding Ceph and Its Purpose

Ceph is a highly scalable distributed storage system designed to provide excellent performance, reliability, and scalability. It is used to manage large amounts of data across a cluster of machines, providing block, object, and file storage in a unified system. One of the key components of Ceph is the Metadata Server (MDS), which is responsible for managing metadata related to the Ceph File System (CephFS).

Identifying the Symptom: MDS Failover Issues

In a Ceph cluster, you might encounter a situation where the MDS failover is not occurring as expected. This can manifest as a lack of automatic failover to standby MDS instances when the active MDS fails, leading to potential downtime or degraded performance of the CephFS.

Exploring the Issue: MDS_FAILOVER

The MDS_FAILOVER issue typically arises due to configuration problems within the Ceph cluster. The failover mechanism is crucial for maintaining high availability of the CephFS, and any misconfiguration can prevent standby MDS instances from taking over when needed. This issue can be caused by incorrect settings in the Ceph configuration files or improperly configured standby MDS instances.

Common Causes of MDS Failover Issues

Standby MDS instances are not properly configured or running.
Incorrect settings in the Ceph configuration files related to MDS.
Network issues preventing communication between MDS instances.

Steps to Resolve MDS Failover Issues

To resolve MDS failover issues, follow these detailed steps:

Step 1: Verify MDS Configuration

Ensure that the MDS configuration in the Ceph configuration file (ceph.conf) is correct. Check for the following settings:

[mds] mds_standby_for_name = <active_mds_name> mds_standby_replay = true

Make sure that standby MDS instances are configured to take over for the active MDS.

Step 2: Check Standby MDS Instances

Ensure that standby MDS instances are running and properly configured. Use the following command to list all MDS instances and their states:

ceph mds stat

Verify that standby MDS instances are in the standby state and ready to take over.

Step 3: Review Network Configuration

Check the network configuration to ensure that all MDS instances can communicate with each other. Network issues can prevent failover from occurring. Use tools like ping or telnet to test connectivity between MDS nodes.

Step 4: Restart MDS Services

If configuration changes were made, restart the MDS services to apply the changes:

systemctl restart ceph-mds.target

Ensure that all MDS instances are restarted and running correctly.

Additional Resources

For more information on configuring and managing Ceph MDS, refer to the following resources:

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