Designing Disaster Recovery Clusters using Metroclusters and Continentalclusters, Reprinted October 2011 (5900-1881)

Figure 2 Failover Scenario with a Single Arbitrator
The scenarios in Table 4, based on Figure 2, illustrate possible results if one or more nodes fail in
a configuration with a single arbitrator.
Table 4 Node Failure Scenarios with One Arbitrator
ResultQuorumFailure
no change4 of 5 (80%)arbitrator 1
pkg A switches4 of 5 (80%)node 1
pkg A and B switch3 of 4 (75%)node 1, then node 2
pkg A and B switch2 of 3 (67%)node 1, 2, then arbitrator 1
cluster halts*1 of 2 (50%)nodes 1, 2, arbitrator 1, then node 3
pkg A switches3 of 4 (75%)arbitrator 1, then node 1
pkg A and B switch to data
center B
3 of 5 (60%)data center A (nodes 1 and 2)
pkg A and B switch, then no
change
2 of 3 (67%)data center A, then arbitrator 1
cluster halts*2 of 5 (40%)data center A and arbitrator 1
cluster halts*1 of 2 (50%)data center A, then arbitrator 1, then node 3
cluster halts*2 of 4 (50%)arbitrator 1, then data center A
cluster halts*2 of 4 (50%)node 3, then data center A
pkg C and D switch to data
center A
3 of 5 (60%)data center B
no change4 of 5 (80%)third location
* Cluster can be manually started with the remaining node.
With a single arbitrator node, the cluster is at risk each time a node fails or comes down for
planned maintenance.
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.
30 Designing a Metrocluster