Ceph MDS_DISK_FULL

The MDS's disk is full, affecting its ability to function properly.
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What is

Ceph MDS_DISK_FULL

 ?

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 computers, offering object, block, and file storage in a unified system. The Metadata Server (MDS) is a critical component in Ceph, responsible for managing the metadata of the Ceph File System (CephFS), which allows users to interact with the storage system as if it were a traditional file system.

Identifying the Symptom: MDS_DISK_FULL

When the MDS's disk becomes full, you may encounter the error code MDS_DISK_FULL. This issue can lead to degraded performance or even a complete halt in the MDS's ability to function, as it cannot write new metadata or manage existing data effectively.

Common Observations

  • CephFS operations become slow or unresponsive.
  • Error messages in the Ceph logs indicating disk space issues.
  • Inability to create new files or directories in CephFS.

Explaining the Issue: MDS_DISK_FULL

The MDS_DISK_FULL error occurs when the disk space allocated to the MDS reaches its capacity. This can happen due to a variety of reasons, such as unexpected data growth, insufficient initial disk allocation, or lack of monitoring and maintenance. When the disk is full, the MDS cannot perform its duties, leading to potential data access issues and system instability.

Root Causes

  • Rapid growth in metadata due to increased file operations.
  • Insufficient disk space allocated during initial setup.
  • Lack of regular monitoring and maintenance of disk usage.

Steps to Resolve MDS_DISK_FULL

To resolve the MDS_DISK_FULL issue, you need to either free up space on the MDS's disk or expand its storage capacity. Here are the steps to achieve this:

Freeing Up Disk Space

  1. Identify and remove unnecessary files or logs from the MDS disk. You can use commands like du and df to analyze disk usage.
  2. Consider archiving old logs or data that are not frequently accessed.
  3. Regularly monitor disk usage to prevent future occurrences. Tools like Grafana can be useful for monitoring.

Expanding Storage Capacity

  1. Attach additional storage to the MDS node. Ensure that the new storage is properly configured and recognized by the system.
  2. Update the Ceph configuration to recognize the new storage. This may involve modifying the ceph.conf file and restarting the MDS service.
  3. Verify that the MDS is now operating with the expanded storage capacity by checking the disk usage again.

Conclusion

Addressing the MDS_DISK_FULL issue is crucial for maintaining the stability and performance of your Ceph cluster. By either freeing up space or expanding storage capacity, you can ensure that the MDS continues to function effectively. Regular monitoring and proactive management are key to preventing such issues in the future. For more detailed guidance, refer to the official Ceph documentation.

Attached error: 
Ceph MDS_DISK_FULL
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