Using Serviceguard Extension for RAC, 4th Edition, February 2007

Introduction to Serviceguard Extension for RAC
Larger Clusters
Chapter 1 31
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” on page 124.
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 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.