Mirroring & Duplexing

As the disk sub-system has its own processor it can be used to provide other services which aid availability.

Disk Mirroring

This is the ability of the disk processor to maintain two copies of the same volume without the Operating System knowing about it. If a hardware problem occurs on the primary copy, the disk processor switches to maintaining the secondary copy, and like ET, rings home for engineering support.

Disk Duplexing

This is like Mirroring, except that the second copy is on a different disk sub-system, this provides insurance not only against disk failure but also of processor failure on the other disk sub-system.