Replacing a failed disk in a Linux RAID configuration involves several steps to ensure that the array remains operational and data integrity is maintained. Below is a step-by-step guide on how to replace a bad disk in a Linux RAID configuration using the mdadm utility:

1. Identify the Failed Disk:
   • Use the mdadm --detail /dev/mdX command to display detailed information about the RAID array.
   • Look for the state of each device in the array to identify the failed disk.
   • Note the device name (e.g., /dev/sdX) of the failed disk.
2. Prepare the New Disk:
   • Insert the new disk into the system and ensure it is recognized by the operating system.
   • Partition the new disk using a partitioning tool like fdisk or parted. Create a Linux RAID (type FD) partition on the new disk.
3. Add the New Disk to the RAID Array:
   • Use the mdadm --manage /dev/mdX --add /dev/sdX1 command to add the new disk to the RAID array.
   • Replace /dev/mdX with the name of your RAID array and /dev/sdX1 with the partition name of the new disk.
   • This command starts the process of rebuilding the RAID array onto the new disk.
4. Monitor the Rebuild Process:
   • Monitor the rebuild process using the mdadm --detail /dev/mdX command.
   • Check the progress and status of the rebuild operation to ensure it completes successfully.
   • The rebuild process may take some time depending on the size of the RAID array and the performance of the disks.
5. Verify RAID Array Status:
   • After the rebuild process completes, verify the status of the RAID array using the mdadm --detail /dev/mdX command.
   • Ensure that all devices in the array are in the “active sync” state and that there are no errors or warnings.
6. Update Configuration Files:
   • Update configuration files such as /etc/mdadm/mdadm.conf to ensure that the new disk is recognized and configured correctly in the RAID array.
7. Perform Testing and Verification:
   • Perform thorough testing to ensure that the RAID array is functioning correctly and that data integrity is maintained.
   • Test read and write operations on the array to verify its performance and reliability.
8. Optional: Remove the Failed Disk:
   • Once the rebuild process is complete and the RAID array is fully operational, you can optionally remove the failed disk from the array using the mdadm --manage /dev/mdX --remove /dev/sdX1 command.
   • This step is optional but can help clean up the configuration and remove any references to the failed disk.

By following these steps, you can safely replace a bad disk in a Linux RAID configuration using the mdadm utility while maintaining data integrity and ensuring the continued operation of the RAID array.