What can you do to recover a RAID 0 array using four disks when one of the disks fails?

RAID 0 (disk striping) provides enhanced performance but no fault tolerance. RAID 0 has more points of failure than a single drive, which means you're more likely to fail than if you only used one hard disk. If one drive fails, the entire set will fail. The only way to recover it is to replace the failing disk and restore from backup. You cannot rebuild the array in the same way that you could with RAID 1 or RAID 5.