If you have a multibus system or a large single-bus system, you should consider using mirrored protection. The greater the number of disk units that are attached to a system, the more frequent disk-related hardware failures are because there are more individual pieces of hardware that can fail. Therefore, the possibility of data loss or loss of availability as a result of a disk or other hardware failure becomes more likely. Also, as the amount of disk storage on a system increases, the recovery time after a disk storage subsystem hardware failure increases significantly. Downtime becomes more frequent, more lengthy, and more costly.