Abstract: A disk drive within a disk array is utilized to capture the original image of data blocks that are updated, i.e., written over, through normal array processes during backup operations. The method captures original data images in a manner that allows the array to be restored to the state that existed at the initiation of the backup process. During execution of backup procedures data is moved in logical block sequence (0 to N) from the array to a backup device, such as a magnetic tape backup device, continuing until all array data has been transferred. Should a write request be received by the disk array controller during backup, the block address associated with the write request is checked to determine if the original data at that address has been written to the backup device. If the original data residing at the target block address has been written to the backup device the write request is scheduled for execution by the array controller.

Abstract: Improved drive logic for a stepper motor is provided using a closed loop feedback system which includes a coded disk driven by the motor and decoding means to derive signals from said disk. The motor is operated at varying speeds in accordance with variations in the lead angle between the energized motor windings and the motor shaft position. Motor drive signals are generated in response to the sensing of leading or trailing edge pulses from the coded disk, and the lead angle, and thus the speed of the motor, may be increased or decreased by selectively shifting the control of the drive signals from a pulse leading edge to a pulse trailing edge or vice versa, thereby providing a change in the lead angle. In addition, pulses from the coded disk may be blanked in order to effect a decrease in motor speed.