1. Make sure the hard disk is well (check by replacing with another new one)
2. When hanging with multiple hard disk, note that the power supply can meet the requirement, monitoring specialized hard disk is more stable with smaller starting current, lower working speed and consume less power than consumer hard disk, if power supply is not enough, the hard disk will not be able to work, which result in disk unrecognized and recording failure.
3. If NVR can read the disk, please format the disk first, as in most cases, repeating read and write will generate disk fragmentation or bad sectors, a formatting process will skip or repair the bad sector.