Error
Error Code:
27
MySQL Error 27: Disk Synchronization Failure
Description
This error indicates that MySQL was unable to write or synchronize data from its internal buffers to the physical disk. It typically occurs when the operating system reports an issue with file system operations, preventing MySQL from ensuring data persistence.
Error Message
Can't sync file '%s' to disk (OS errno %d - %s)
Known Causes
4 known causesDisk Space Exhaustion
The storage volume where MySQL attempts to write or synchronize data has run out of free space.
Insufficient File Permissions
The MySQL process does not have the necessary operating system permissions to write or synchronize files to disk within its data directory.
Underlying Storage System Failure
An issue with the physical disk, RAID array, network storage, or the operating system's file system is preventing write operations.
File System Lock or Corruption
The target file might be locked by another process, or the file system itself is in an inconsistent state, preventing MySQL from syncing.
Solutions
3 solutions available1. Verify Disk Space and Permissions easy
Ensure the MySQL data directory has sufficient free space and appropriate write permissions.
1
Check available disk space on the partition where your MySQL data directory resides.
df -h2
Identify the MySQL data directory. This is typically found in your `my.cnf` or `my.ini` file, often under `datadir`.
grep datadir /etc/mysql/my.cnf # Or similar path for your OS3
Verify write permissions for the MySQL user on the data directory and its subdirectories.
ls -ld /var/lib/mysql # Replace with your actual datadir4
If permissions are incorrect, change them. The MySQL user (often `mysql`) should have ownership and write access.
sudo chown -R mysql:mysql /var/lib/mysql # Replace with your actual datadir
sudo chmod -R u+w /var/lib/mysql5
Restart the MySQL service to apply changes and test.
sudo systemctl restart mysql # Or mysqld, depending on your OS2. Inspect Underlying Storage System medium
Investigate potential issues with the physical or virtual disk, RAID array, or network storage.
1
If using physical disks, check the health of the disk using SMART tools.
sudo smartctl -a /dev/sda # Replace /dev/sda with your disk device2
If using a RAID array, check the status of the array for any degraded or failed drives.
sudo mdadm --detail /dev/md0 # Replace /dev/md0 with your RAID device3
For virtual machines or cloud instances, check the storage provider's health status and logs for any reported issues.
Refer to your cloud provider's documentation for storage monitoring and diagnostics.4
Examine system logs (e.g., `/var/log/syslog`, `/var/log/messages`) for any disk-related errors or warnings that might coincide with the MySQL error.
sudo tail -f /var/log/syslog5
If disk errors are found, consult your system administrator or storage vendor for hardware replacement or repair.
N/A3. Review MySQL Configuration and I/O Tuning medium
Adjust MySQL's I/O-related configuration parameters for better stability.
1
Locate your MySQL configuration file (`my.cnf` or `my.ini`).
grep datadir /etc/mysql/my.cnf # Use this to find the datadir, the config file is usually nearby or the same path.2
Consider adjusting `innodb_flush_method`. For some file systems, `O_DIRECT` can improve performance and reliability by bypassing the OS buffer cache.
[mysqld]
innodb_flush_method = O_DIRECT3
Review `innodb_flush_log_at_trx_commit`. Setting this to `2` (flush to OS cache, but not necessarily to disk until fsync) can reduce disk writes and potentially mitigate sync issues, but at a slight risk of data loss in case of OS crash.
[mysqld]
innodb_flush_log_at_trx_commit = 24
If you have a fast SSD, `innodb_io_capacity` can be tuned higher to allow InnoDB to utilize the disk's I/O capabilities more aggressively.
[mysqld]
innodb_io_capacity = 2000 # Adjust based on your disk performance5
After making changes to the configuration file, restart the MySQL service.
sudo systemctl restart mysql # Or mysqld