SCSI stands for Small Computer System Interface. It is the second-most popular hard disk interface used in PCs today. Many companies use SCSI hard drives because the interface allows for much faster data transfer speeds. One of the main differences with a SCSI hard drive and an ATA hard drive is a SCSI disk must have an independent controller for it to communicate with the operating system.
Although SCSI controller has many benefits, it still adds another layer, another chance for failure and data loss. Unlike the IDE counterparts, SCSI disks operate through their own SCSI BIOS. When the computer is powered up, the SCSI BIOS sends a “Start Unit Request” command to the SCSI devices under its control. If the drive fails to start correctly, the SCSI drive will (often) power down and the error “Start Unit Request Failed” is displayed.
Which caused the SCSI drive failure?
Power down / power up: SCSI drives are often found in machines that “never” switch off. When eventually these machines are powered down, getting the SCSI drives to restart can often be difficult
Electronic Failure: Failure of the electronic circuitry on the hard disk will prevent the drive from starting, fortunately drives with this type of failure are often recoverable
Mechanical Failure: Often characterized by a clucking sound or high pitched whine, SCSI hard disk mechanical failures are often the worst type of failure these drives can suffer. The noises, though not always apparent, are indicative of an internal mechanical failure or head crash.
All the usual failures that can be found on hard disk drives e.g. bad sectors, logical corruption etc.