Partial Failover

The fact that one physical host can master multiple logical hosts permits partial failover of data services. Figure 1-24 shows a star configuration that includes three physical hosts and five logical hosts. In this figure, the lines connecting the physical hosts and the logical hosts indicate which physical host currently masters which logical host (and disk groups).

The four logical hosts mastered by phys-hahost1 (solid lines) can fail over individually to the hot-standby server. Note that the hot-standby server in Figure 1-24 has physical connections to all multihost disks, but currently does not master any logical hosts.

Figure 1-24 Before Partial Failover With Multiple Logical Hosts

Figure 1-25 shows the results of a partial failover where hahost5 has failed over to the hot-standby server.

During partial failover, phys-hahost1 relinquishes mastery of logical host hahost5. Then phys-hahost3, the hot-standby server, takes over mastery of this logical host.

Figure 1-25 After Partial Failover With Multiple Logical Hosts

You can control which data services fail over together by placing them on the same logical host. Refer to Chapter 2, Planning the Configuration, for a discussion of the issues associated with combining or separating data services on logical hosts.