Hard Partitioning: Dynamic Domains - Oracle Solaris 10 System Virtualization Essentials - page 46

IOU resides in a single domain, Figure 2.1 shows that the PCIe cards should be
installed from the bottom up to reduce any possible bottlenecks with the boot
drives and built-in Ethernet.
Because the M5000 can support two IOU trays, it is possible for the number of
domains to grow to 4. Thus the first domain assigned to the second IOU is just like
the first domain assigned to the first IOU—that is, filled with several interfaces
and internal boot drives. The second domain on the second IOU is just like the
second domain on the first IOU, which has only two PCIe slots.
The M8000/M9000 block diagram in Figure 2.2 shows similar components to
that of the M4000/M5000. The board that contains the CPUs and memory is the
CPU/memory unit (CMU). Because the system contains more than two CMU
boards, crossbar board units (XBU) are used to provide point-to-point (board-to-
board) private communications, depending on the domain configurations. This
diagram also shows a slightly different pathway to the SC because of the ability
to grow to 4, 8, or 16 system boards. The crossbar allows domain performance to
scale as more boards are added to the domain. Domain performance is not affected
by the behavior of other domains. The crossbar also provides for domain isolation
in the event of faulty CMU or IOU boards. Only the domain with the faulty hard-
ware is affected; the other domains continue to run normally.
Figure 2.2 Block Diagram of M8000/M9000