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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An OSD's disk is experiencing I/O errors, affecting its ability to store data.

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The RADOS Gateway service is not running, which could be due to network issues, resource constraints, or configuration errors.

Ceph Network congestion is affecting OSD communication, leading to performance degradation.

Network congestion is affecting OSD communication, leading to performance degradation.

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PGs are undergoing backfill operations, often due to OSD additions or recoveries.

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A monitor is experiencing high CPU usage, affecting its performance.

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An OSD is experiencing high CPU usage, affecting its performance.

Ceph Authentication failures when accessing the RADOS Gateway.

Incorrect credentials or configuration settings.

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A monitor is consuming excessive memory, possibly due to a memory leak.

Ceph High network latency is affecting OSD performance.

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A requested bucket does not exist in the RADOS Gateway.

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The MDS is consuming excessive memory, possibly due to a memory leak.

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An OSD's disk has failed, affecting its ability to store data.

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PGs are incomplete, often due to missing OSDs or data corruption.

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A monitor daemon has crashed, possibly due to software bugs or resource exhaustion.

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The journal size is insufficient for the current workload, or there may be a configuration issue.

Ceph POOL_NOT_FOUND

A requested pool does not exist, possibly due to configuration errors or deletion.

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Network issues are affecting OSD communication, leading to degraded performance or failures.

Ceph An OSD is repeatedly going up and down, often due to unstable hardware or network issues.

Unstable hardware or network issues causing OSD flapping.

The RADOS Gateway is experiencing slow performance, possibly due to high load or resource constraints.

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Ceph OSD daemon crash

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PGs are not in a clean state, often due to OSD failures or ongoing recovery operations.

Ceph Monitor disk is full, causing operational issues.

The monitor's disk has reached its storage capacity limit.

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A client is using an incompatible version of the Ceph software.

Ceph SLOW_REQUESTS

Requests to the cluster are slow, possibly due to high load or resource contention.

Ceph RADOSGW_UNAVAILABLE

The RADOS Gateway (RGW) is unavailable, affecting object storage access.

Ceph MDS failover is not occurring as expected.

Configuration issues with MDS or improperly configured standby MDS instances.

The Metadata Server (MDS) is down, affecting CephFS operations.

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A network partition is causing communication issues between Ceph components.

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Errors in the CRUSH map configuration, potentially causing data placement issues.

Ceph Authentication failure between Ceph components.

Incorrect keyring or configuration settings.

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An OSD has reached its full capacity, preventing further writes.

Operations are taking longer than expected, possibly due to high load, network latency, or hardware bottlenecks.

Ceph MON_QUORUM_LOST

The monitor quorum is lost, often due to network partitions or multiple monitor failures.

PGs are stuck in a non-active state, possibly due to OSDs being down or network partitions.

Ceph PG_DEGRADED

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Ceph An OSD is marked as out, meaning it is not part of the active cluster and not serving data.

The OSD might be down or manually marked out due to maintenance or failure.

Ceph An OSD is marked as down in the Ceph cluster.

Network issues, hardware failure, or the OSD daemon crashing.

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