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 4 131

Example Failover Scenarios with One Arbitrator

Taking a node off-line for planned maintenance is treated the same as a

node failure in these scenarios. Study these scenarios to make sure you

do not put your cluster at risk during planned maintenance.

Figure 4-2 Failover Scenario with a Single Arbitrator

The scenarios in Table 4-3 are based on Figure 4-2 and illustrate possible

results if one or more nodes fail in a configuration with a single

arbitrator.

node 1

pkg A

Data Center A

node 2

pkg B

SRDF links

Third Location

node 3

pkg C

Data Center B

node 4

pkg D

arbitrator 1

Table 4-3 Node Failure Scenarios with One Arbitrator

Node Failure Quorum Result

arbitrator 1 4 of 5 (80%) nothing

node 1 4 of 5 (80%) pkg A switches

node 1, then node 2 3 of 4 (75%) pkg A and B

switch

node 1, 2, then arbitrator 1 2 of 3 (67%) nothing

nodes 1, 2, arbitrator 1, then

node 3

1 of 2 (50%) cluster halts*

arbitrator 1, then node 1 3 of 4 (75%) pkg A switches