A disk drive storage system comprises an array of disk drive units (230). The disk drives (160) contained in the units have a diameter of 65mm and rotate at 10,000 RPM which has the effect of reducing latency. In a preferred embodiment data and corresponding parity information are converted into portions and stored on a respective different one of the disk drive units. Data stored on a filed disk drive unit can be regenerated on a replacement disk drive unit. A disk drive unit can be replaced without powering down the system. Four disk drive units can be arranged in a four drive system to match the space geometry of the traditional half-high flexible disk drive used in a personal computer.