Compaq manual Using Multiple-Bus Failover Mode, 30Configuring an HSZ80 Array Controller

2–30Configuring an HSZ80 Array Controller

■For better subsystem performance, balance your assignment of target ID numbers across your dual-redundant pair of controllers. For example, if you are presenting four targets to the host, prefer two to one controller and two to the other controller.

■Balance your assignment of devices. For example, in an 18-device subsystem, place 3 devices on each of the 6 ports, rather than placing 6 devices on each of 3 ports.

■The controller to which you copy configuration information restarts after you enter the SET FAILOVER command.

Using Multiple-Bus Failover Mode

Multiple-bus (or host-assisted) failover is a dual-redundant controller configuration in which each controller has its own connection to the host. Thus, if one of the host connections to a controller fails, the host can cause units that became inaccessible to failover to the remaining viable connection. Because both controllers service the same storage units, either controller can continue to service all of the units if the other controller fails.

Keep the following points in mind when configuring controllers for multiple-bus failover:

■The host distributes the I/O load between the controllers.

■The host must have two SCSI adapters as well as operating-system software to support the multiple-bus failover, dual-redundant controller configuration.

■SCSI target ID number and LUN configurations on each controller must be identical.

■Mount both controllers in the same BA370 rack-mountable enclosure and follow the steps in “Configuring an HSZ80 Array Controller,” page 2–3.

■Partitioning is not supported.