Dell AX4-5 - Manual (Page 47)

Understanding Your Failover Cluster
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N + I Failover
N + I failover is an active/passive policy where dedicated passive cluster
node(s) provide backup for the active cluster node(s). This solution is best for
critical applications that require dedicated resources. However, backup nodes
add a higher cost of ownership because they remain idle and do not provide
the cluster with additional network resources.
Figure 4-1 shows an example of a 6 + 2 (N + I) failover configuration with six
active nodes and two passive nodes. Table 4-5 provides an N + I failover
matrix for Figure 4-1.
Table 4-4. Windows Server 2008 Failover Policies
Failover
Policy Description Advantage Disadvantage(s)
N + I One or more nodes
provides backup for
multiple systems. Highest
resource
availability. • May not handle more than
one backup node failure.
• May not fully utilize all of
the nodes.
Failover pair Applications can
failover between the
two nodes.
Easy to plan the
capacity of each
node. Applications on the pair
cannot tolerate two node
failures.
Multiway Running applications
migrate to multiple
nodes in the cluster.
Application
load-balancing. Must ensure that the
failover nodes have ample
resources available to handle
the additional workload.
Failover ring Running applications
migrate to the next
preassigned node.
Easy to scope
node capacity
for one server
failure. The next node for failover
may not have ample
resources to handle the
workload.