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Hard Disk Drive Controller

A vital component required for the correct operation of a hard disk drive is the controller board, which manages the interface between the hard disk and the host computer or RAID array backplane or controller. The controller board must be functioning perfectly in order to avoid the hard disk drive malfunctioning, such as the spindle motor rotating at the incorrect speed, the read/write heads not being positioned correctly or the defect lists not be used, which lead to the wrong sectors being returned by the hard disk drive.

In the early days each hard disk drive came with a separate dedicated controller card which fitted into the peripheral slot of the host computer’s motherboard. Hard disks needed to be low level formatted in order to ensure that the controller card could update the defect list, which the data returned by the drive could appear to be corrupt. The use of hard disks to create a RAID array only became a viable proposition once the controller card became an integral part of the hard disk drive itself.

Defect List Management

The correct management of the defect lists is extremely important, as they are used to map out unreadable bad sectors so that they are no longer used for storing data. These must be accessible and maintained properly to ensure that the correct sectors are always accessed. There are two defect list, the primary list (P-List) and the growth defect list (G-list).

The primary defect list is created when the hard disk drive is low level formatted in the factory, during which any unreadable bad sector is entered into this list to ensure it is never used. This list shifts the sectors by one for every bad sector marked so that the good sectors are regarded as a single contiguous run of data. Once created, this list is not changed, unless another low level format is initiated.

When the drive is being used and unreadable bad sector is encountered an attempt is made to recover the data, which moved into an area of the disk containing spare sectors. The bad sector and its position within the spare sector area is placed into the grown defect list ensuring that the correct sector is always used.

It is easy to see that if the defect lists are not maintained correctly, become inaccessible or corrupted, the wrong sectors may be returned by the drive. If the P-List is lost or damaged, this could cause a shift in the sectors read for each bad sector and makes the data recovery process very complex. Such an error is, fortunately rare.

Hard Drive Firmware

The firmware chip on a hard drive controller board is the equivalent of a brain and must function correctly otherwise the disk could become inaccessible, or behave in a seemingly random fashion. Firmware damage is often the result of high temperatures, but other possible failure mechanisms include power surges and static damage from incorrect handling. When the firmware fails, depending upon the drive manufacturer and model of drive it can behave in one of many ways, such as not appear at all, return a reduced capacity or display a different device identifier string.

Each model of drive will during its lifetime see the manufacturer updates the firmware over time, so that two apparently identical drives may be different. If the drive firmware needs to be replaced, the donor chip must be same firmware revision, as different versions are usually incompatible, otherwise the drive will fail to function correctly.

Controller Board Data Recovery

Failure of the hard disk controller board in RAID arrays is most likely to occur through overheating, often as the result of air disruption. RAID arrays are very likely to be protect by surge protectors, although damage to the drive from a power surge can still occur, which usually damages the voltage regulator. In rare instances a drive controller board can happen through mishandling of the drive causing a static shock, which may damage electronic component.

If the controller board of a hard disk fails in a RAID array it is important that if redundancy is used, it is replaced and the RAID rebuilt. If there is no redundancy or the RAID array fails due to another drive or drives failing, you should power the system down before further damage can result. You should then contact a professional data recovery service, such as DiskEng. Under no circumstances should you attempt to replace the controller board, as it is unlikely to succeed and even if it does run, the reintroduction of this drive to the RAID array could cause corruption of the data.

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