If the drive controller is failing or non-functional, it can be repaired by replacing the controller board with a new one with the appropriate ROM, however the process may cost more than a new hard drive. If the connections are bad they should be inspected to ensure it's something simple, and not cracked traces on the controller card. Controller failures are relatively rare unless there's a manufacturing or design defect.
Scannerz may be able to isolate problems with the connections between the controller and the system, however if the controller itself is non-functional, for all practical purposes the drive is "turned off" and won't be seen by anything, including Scannerz.
The Drive Heads, Platter, and Actuator Arm
Data is written to and read from the drive platters via the drive's heads, which are positioned via an actuator arm. The actuator arm behaves in a manner similar to the tone arm on a record player, but it's constantly moving around on the platter at very high speeds. The drive platters are coated with a magnetically modifiable material that can be used to store information based on the localized magnetic state of a region of the platter. The information on the platters is broken down into what are called cylinders and sectors, along with tracking and positioning information. The tracking information is read by the drive heads and interpreted by the drive controller to position the drive heads to the regions of the platter that will eventually be used to read or write data on the platter.
During a write operation, after the controller positions the drive's heads over the appropriate region of the drive, the surface of the platter is modified by inducing an electromagnetic field over specific regions of the platter surface. During a read operation, the spinning nature of the platter is able to induce a current into the heads much in the same way that a moving magnet can induce a current into a wire. The storage unit on the platter is the sector, which typically stores 512 bytes of information, although newer drives may have sector sizes of 4 kilobytes.
The most common problem with the heads, platter, and actuator arm is damage to the surface of the platter during a head crash. This may be caused by impact or by contamination of the drive chamber by foreign substances. As a drive ages it may start losing its ability to retain information. If the actuator arm jams or loses it's connections, the drive will become completely dysfunctional, possibly damaging the platter in the process. If the actuator arm is marginally functional, it may start increasingly damaging the drive platters as the heads collide with the platters.
A hard drive head crash will leave sections of the drive either unreadable (bad sectors,) marginally readable (weak sectors,) or both. This will often cause considerable delays as the system tries to read data from the damaged areas. Bad sectors will always generate I/O errors that are repeatable during a surface scan. Weak sectors will be readable, but will generate delays or timing irregularities that will occur consistently at the exact same locations during surface scan tests. Weak sectors can prove to be nearly as problematic as bad sectors. If the actuator arm fails or the heads start binding on the platter, the drive will become completely unusable very quickly. If the actuator arm is allowing the heads to scrape the platter surface it's typically accompanied by squealing or grinding sounds.
Contemporary hard drives come with a set of spare sectors that can be used to replace bad sectors if the controller detects them. If a hard drive detects a bad sector, it can be re-mapped to a spare sector if one is available, but the data contained in the original bad sectors cannot be recovered. Weak sectors may be able to have data recovered, but in some cases it may be corrupt. Weak sectors may or may not be remapped to spare sectors, depending on how severely damaged the sector is. Weak sectors may start appearing somewhat rampantly as a drive ages, especially if the drive is taken out of service, put into storage, and then put back into use after a few years.
A user may be able to correct problems with a drive with bad or weak sectors by reformatting the drive with an option to write data, usually binary zeros, to every sector on the drive. During the formatting and zeroing process, the drive controller will attempt to remap the bad sectors to spare sectors, as long as spares are available. If the supply of spare sectors becomes exhausted, the drive should, in our opinion, be considered unusable. Remapping bad sectors to spare sectors is a reasonable approach if only a few sectors are damaged, but if the damage is widespread we recommend replacing the drive.
When using Scannerz, bad and/or weak sectors are typically detected during a Normal Mode scan and confirmed during a Diagnostic Mode scan. Confirming bad or weak sectors is important because problems with bad cables or connectors can produce similar results if not confirmed.
The steps for performing these tests are as follows: