Using Serviceguard Extension for RAC, 8th Edition, March 2009

Figure 1-5 Four-Node RAC Cluster
In this type of configuration, each node runs a separate instance of RAC and may run one or
more high availability packages as well.
The figure shows a dual Ethernet configuration with all four nodes connected to a disk array
(the details of the connections depend on the type of disk array). In addition, each node has a
mirrored root disk (R and R'). Nodes may have multiple connections to the same array using
alternate links (PV links) to take advantage of the array's use of RAID levels for data protection.
Alternate links are further described in the section “Creating RAC Volume Groups on Disk
Arrays ” (page 83).
Point to Point Connections to Storage Devices
Some storage devices allow point-to-point connection to a large number of host nodes without
using a shared SCSI bus. An example is shown in Figure 1-6, a cluster consisting of eight nodes
with a FibreChannel interconnect. (Client connection is provided through Ethernet.) The nodes
access shared data on an HP StorageWorks EVA or XP series or EMC disk array configured with
16 I/O ports. Each node is connected to the array using two separate Fibre channels configured
with PV Links. Each channel is a dedicated bus; there is no daisy-chaining.
24 Introduction to Serviceguard Extension for RAC