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 4 133
Example Failover Scenarios with Two Arbitrators
Having two arbitrator nodes adds extra protection during nodes failures
and allows you to do planned maintenance on arbitrator nodes without
losing the cluster should a disaster occur.
Figure 4-3 Failover Scenario with Two Arbitrators
The scenarios in Table 4-5 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
SRDF 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 4-5 Data Center Failure Scenarios with Two Arbitrators
Node 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
nothing
data center A and arbitrator
1
3 of 6 (50%) cluster halts*
data center A, then arbitrator
1, then node 3
2 of 3 (67%) pkg A, B, and C switch