State database replicas provide redundant data about the overall Solaris Volume Manager configuration. The following example, drawing on the sample system provided in Chapter 5, Configuring and Using Solaris Volume Manager (Scenario), describes how state database replicas can be distributed to provide adequate redundancy.
The sample system has one internal IDE controller and drive, plus two SCSI controllers, which each have six disks attached. With three controllers, the system can be configured to avoid any single point-of-failure. Any system with only two controllers cannot avoid a single point-of-failure relative to Solaris Volume Manager. By distributing replicas evenly across all three controllers and across at least one disk on each controller (across two disks if possible), the system can withstand any single hardware failure.
A minimal configuration could put a single state database replica on slice 7 of the root disk, then an additional replica on slice 7 of one disk on each of the other two controllers. To help protect against the admittedly remote possibility of media failure, using two replicas on the root disk and then two replicas on two different disks on each controller, for a total of six replicas, provides more than adequate security.
To round out the total, add 2 additional replicas for each of the 6 mirrors, on different disks than the mirrors. This configuration results in a total of 18 replicas with 2 on the root disk and 8 on each of the SCSI controllers, distributed across the disks on each controller.