State database replicas provide redundant data about the overall Solaris Volume Manager configuration. The following example, is based on the sample system in the scenario provided in Chapter 5, Configuring and Using Solaris Volume Manager (Scenario). This example 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. Each SCSI controller has 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.
In a minimal configuration, you 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, add another replica to 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 provide even more security, add 12 additional replicas spread evenly across the 6 disks on each side of the two 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.