Disk repair is usually not cost-effective. However, in this case, the disk capacity was a massive 14TB Western Digital (market price starting from €600). According to the client, others refused even to take a look. After thorough diagnostics, a controller failure due to voltage fluctuations (likely caused by incorrect connection) was identified. After obtaining a controller from an identical disk and adapting its firmware, the drive is now fully functional and was returned to the client.