netdata/health/guides/btrfs/btrfs_device_generation_errors.md

Understand the alert

This alert is about BTRFS generation errors. When you receive this alert, it means that your BTRFS file system has encountered errors during its operation.

What are BTRFS generation errors?

BTRFS is a modern copy-on-write (CoW) filesystem, which is developed to address various weaknesses in traditional Linux file systems. It features snapshotting, checksumming, and performs background scrubbing to find and repair errors.

A BTRFS generation error occurs when the file system encounters issues while updating the data and metadata associated with a snapshot or subvolume. This could be due to software bugs, hardware issues, or data corruption.

Troubleshoot the alert

1. Verify the issue: Check your system logs for any BTRFS-related errors to further understand the problem. This can be done using the dmesg command:

   sudo dmesg | grep BTRFS
   

2. Check the BTRFS filesystem status: Use the btrfs filesystem command to get information about your BTRFS filesystem, including the UUID, total size, used size, and device information:

   sudo btrfs filesystem show
   

3. Perform a BTRFS scrub: Scrubbing is a process that scans the entire filesystem, verifies the data and metadata, and attempts to repair any detected errors. Run the following command to start a scrub operation:

   sudo btrfs scrub start -Bd /path/to/btrfs/mountpoint
   

The -B flag will run the scrub in the background, and the -d flag will provide detailed information about the operation.

1. Monitor scrub progress: You can monitor the scrub progress using the btrfs scrub status command:

   sudo btrfs scrub status /path/to/btrfs/mountpoint
   

2. Analyze scrub results: The scrub operation will provide information about the total data scrubbed, the number of errors found, and the number of errors fixed. This information can help you determine the extent of the issue and any further action required.

3. Address BTRFS issues: Depending on the nature of the errors, you may need to take further action, such as updating the BTRFS tools, updating your Linux kernel, or even replacing faulty hardware to resolve the errors.

4. Set up a regular scrub schedule: You can schedule regular scrubs to keep your BTRFS filesystem healthy. This can be done using cron. For example, you can add the following line to /etc/crontab to run a scrub on the 1st of each month:

   0 0 1 * * root btrfs scrub start -B /path/to/btrfs/mountpoint
   

Useful resources

1. BTRFS Wiki Homepage
2. Btrfs Documentation