The hard disk drive controller is a critical component which provides the interface between the hard disk and the host computer or RAID array controller. If the controller board fails to operate correctly it can result in erratic behaviour which could lead to damage occurring to components of the hard disk.
In a correctly functioning drive the controller board positions the read/write heads in order to read the right sectors and ensures the spindle motor rotates at the pre-determined speed. The firmware and maintenance data is stored on the controller board, which includes the defect lists. If the controller board malfunctions the best option for recovering your data is to send the hard disk to a professional data recovery company.
Sector Defect Lists
The position of each defect is important, particular any unreadable bad sector located during the factory format process, each one stored in the primary defect list (P-List). Bad sectors encountered during the normal operation of the drive are stored in the growth defect list (G-List). In the event of either defect list becoming inaccessible or corrupt, incorrect sectors will be returned by the drive.
The contents of the primary defect list are created during the low level factory format process. This list is of the utmost importance, as the location of sectors is shifted by one for each unreadable bad sector. This list must not be changed once created, as any change may lead to the incorrect sectors being returned.
During the normal operation of the drive, any unreadable bad sector detected is an attempt is made to recover it before the contents are stored in the spare sector area of the drive. The location of the original sector and the location in the swap area are stored in the G-List.
The firmware is microcode stored on the drive controller board, the correct functioning of which ensures the drive continues to operate normally. Any error in the firmware can result in random behaviour of the drive. A failure of the firmware is often the result of the drive operating at high temperatures, power surges or static damage due to incorrect handling of the hard disk.
In most drives this will result in them not showing up in the BIOS, although some drives will still be found, but display a different identification string and capacity. The drive must be sent to a professional data recovery company, who can use a donor board in order to overcome the problem, a complex procedure which should only be undertaken a qualified data recovery specialist. It is also important that the correct version of the firmware is used, otherwise incorrect sectors may be returned.
Data Recovery After Controller Failure
The failure of the hard drive controller board is a fairly common issue, usually the result of overheating, very often the result of inadequate airflow across the disk. Although servers and RAID arrays usually employ surge protection and uninterruptible power supplies, power surges can still cause damage, albeit a rare occurrence for such a setup. Incorrect handling of the drive due to inadequate static precaution, again rare in a server environment, may also cause damage to the controller board.
For any disk which is part of a RAID employing redundancy, the drive should be replaced and rebuilt before the RAID goes offline. Should your RAID or the drive in your server fail, they should be sent for data recovery to a professional company such as DiskEng. Attempts to recovery the data yourself could result in further damage, causing data loss.