Standard disk unit mirroring support requires that both disk units of the load source mirrored pair (unit 1) are attached to load source IOP. This allows the system to IPL from either load source in the mirrored pair and allows the system to dump main storage to either load source if the system ends abnormally. However, since both load sources must be attached to the same IOP, the best mirroring protection possible for the load source mirrored pair is IOA-level protection. To provide a higher level of protection for your system, you can use remote load source mirroring and remote disk unit mirroring.
Remote disk unit mirroring support, when combined with remote load source mirroring, mirrors the disk unit on local optical buses with the disk unit on optical buses that terminates at a remote location. In this configuration, the entire system, including the load source, can be protected from a site disaster. If the remote site is lost, the system can continue to run on the disk unit at the local site. If the local disk unit and system unit are lost, a new system unit can be attached to the set of disk units at the remote site, and system processing can be resumed.
Remote disk unit mirroring, like standard disk unit mirroring, supports mixing device-parity-protected disk units in the same disk pool with mirrored disk units; the device parity disk unit can be located at either the local or the remote site. However, if a site disaster occurs at the site containing the device parity disk unit, all data in the disk pools containing the device parity disk unit is lost.
Remote mirroring support makes it possible to divide the disk units on your system into a group of local disk units and a group of remote disk units. The remote disk units are attached to one set of optical buses and the local disk units to another set of buses. The local and remote disk units can by physically separated from one another at different sites by extending the appropriate optical buses to the remote site. The distance between the sites is restricted by the distance that an optical bus may be extended.
If you decide that remote disk unit mirroring is needed for your system, you need to Prepare your system for remote mirroring and then Start site-to-site mirroring.