Designing Disaster Tolerant High Availability Clusters, 10th Edition, March 2003 (B7660-90013)

Building a Metropolitan Cluster Using MetroCluster/SRDF
Designing a Disaster Tolerant Architecture for use with MetroCluster/SRDF
Chapter 4128
the EMC Symmetrix disk array in data center A is the R1 disk for
packages A and B, and the R2 disk for packages C and D in data center
B. Likewise the EMC Symmetrix disk array in data center B is the R1 for
packages C and D, and the R2 for packages A and B.
Arbitrators provide similar functionality to the cluster lock disk, and act
as tie-breakers for a cluster quorum in case all of the nodes in one data
center go down at the same time. Cluster lock devices are not supported
in MetroCluster configuration because cluster locks cannot be
maintained across the SRDF link.
Arbitrators are fully-functioning systems that are members of the cluster
and are not usually physically connected to the Symmetrix units.
Table 4-1 lists the allowable number of nodes at each main data center
and the third location, assuming a 16-node maximum cluster size.
Figure 4-1 on page 127 shows a two data center and third location
configuration with two nodes at each site, and two arbitrator nodes
Table 4-2 Possible Number of Nodes in a Three Data Center Configuration
Primary Data
Center A
(with
Symmetrix)
Primary Data
Center B
(with
Symmetrix)
Arbitrator Third
Location
(No Symmetrix)
11 1
22 1
22 2*
33 1
21 2
33 2*
44 1
44 2*
55 1
55 2*
66 1