Failover and failback support – Dell PowerVault 775N (Rackmount NAS Appliance) User Manual
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Cluster configurations may include both active and passive cluster nodes. Active nodes are the primary nodes in the cluster.
These nodes support the cluster workload by processing application requests and providing client services. Passive nodes are
backup nodes that support the active nodes if a hardware or software failure occurs, ensuring that client applications and
services are highly available.
NOTE:
Passive nodes must be configured with the appropriate processing power and storage capacity to support the
resources that are running on the active nodes.
An active/active (active
x
) configuration is a cluster with virtual servers running separate applications or services on each
node. When an application is running on node 1, the remaining cluster node does not have to wait for node 1 to fail. The
remaining cluster node can run its own cluster-aware applications (or another instance of the same application) while
providing failover capabilities for the resources on node 1. This configuration requires careful planning to ensure that adequate
resources are available on each node to handle the increased load if one node fails.
An active/passive (active
x
/passive
x
) configuration is a cluster where an active cluster node is processing requests for a
clustered application while the passive cluster node simply waits for the active node to fail. For example, N + I failover
(where N = the number of active nodes and I = the number of inactive [or passive] nodes) is an active/passive failover policy
where a dedicated, passive cluster node provides backup for the active cluster node.
Active/passive configurations are more costly in terms of price and performance because the passive cluster node remains idle
all of the time. This configuration is appropriate for business-critical systems because the application can use all of the
resources of a standby cluster node if one active cluster node fails.
provides a description of some active/passive configuration types.
Table 1-6. Active/Passive Configuration Types
Configuration
Type
Active Cluster
Node(s)
Passive Cluster
Node(s)
Description
Active
1
/Passive
1
1
1
The active node(s) processes requests while the passive node
waits for the active node to fail.
Active
2
/Passive
1
2
1
Active
2
/Passive
2
2
2
Active
3
/Passive
1
3
1
Active
3
/Passive
2
3
2
Active
4
/Passive
1
4
1
Active
4
/Passive
2
4
2
Active
5
/Passive
1
5
1
Active
5
/Passive
2
5
2
Active
6
/Passive
1
6
1
Active
6
/Passive
2
6
2
Active
7
/Passive
1
7
1
Failover and Failback Support
One of the key features of Cluster Service is failover and failback support. Failover is the process of automatically moving
resources from a failed cluster node to another cluster node. Failback is the process of moving the resources back to the
original cluster node (if required). Failback can be an automatic or manual process, depending on how you configure the