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

Building a Metropolitan Cluster Using MetroCluster/CA
Designing a Disaster Tolerant Architecture for use with MetroCluster/CA
Chapter 3 81
Example Failover Scenarios with Two Arbitrators
Having two arbitrator nodes adds extra protection during node failures
and allows you to do planned maintenance on arbitrator nodes without
losing the cluster should a disaster occur.
Figure 3-3 Failover Scenario with Two Arbitrators
The scenarios in Table 3-5 illustrate possible results if a data center or
one or more nodes fail in a configuration with two arbitrators. Note that
3 of the 4 scenarios that caused a cluster halt with a single arbitrator, do
not cause a cluster halt with two arbitrators.
node 1
pkg A
Data Center A
node 2
pkg B
A
B
D
1
C
1
CA links
arbitrator 1
Third Location
node 3
pkg C
Data Center B
node 4
pkg D
C
D
B
1
A
1
arbitrator 2
Table 3-5 Failure Scenarios with Two Arbitrators
Failure Quorum Result
data center A (nodes 1 and 2) 4 of 6 (67%) pkg A and B switch
to data center B
data center A, then arbitrator
1
3 of 4 (75%) pkg A and B switch,
then no change
data center A and arbitrator 1 3 of 6 (50%) cluster halts*