Understanding and Designing Serviceguard Disaster Recovery Architectures

However, when you use two arbitrator nodes in the third location, you can place one node in one
datacenter and two nodes in another datacenter.
Table 1 lists the allowable number of nodes at each main data center and the third location, up
to a 16-node maximum cluster size.
Table 1 Supported System and Data Center Combinations (Applicable to Serviceguard Version
11.16 or later)
Possible Cluster Arbitration types in
Data Center C
Number of Nodes in Data Center BNumber of Nodes in Data Center A
1 Arbitrator Node or Quorum Server11
2 Arbitrator Nodes21
2 Arbitrator Nodes12
1 Arbitrator Node or 2 Arbitrator
Nodes* or Quorum Server System
2 to 7 (same number of nodes in Data
Center A and Data Center B)
2 to 7 (same number of nodes in Data
Center A and Data Center B)
Quorum Server System88
* Configurations with two arbitrators are preferred because they provide a greater degree of
availability, especially in cases when a node is down due to a failure or planned maintenance.
The following is a list of recommended arbitration methods for Metrocluster solutions in order of
preference:
• Two arbitrator nodes, where supported
• One arbitrator node, where supported
• Quorum Server with HP Auto Port Aggregation
• Quorum Server
For more information on Quorum Server, see HP Serviceguard Quorum Server Release Notes
available at http://www.hp.com/go/hpux-serviceguard-docs—> HP Serviceguard Quorum Server
Software.
Features of Metrocluster
Metrocluster across subnets
Specifically for disaster recovery, Serviceguard clusters or data centers can also be configured on
different subnets. Such configurations provide improved scalability.
The following are the guidelines that must be followed to configure a Serviceguard cluster across
network subnets:
• All the nodes in the cluster must belong to the same domain.
• The latency period in the heartbeat network that is configured across subnets must be less
than 200 milliseconds.
• A minimum of two heartbeat subnets must be configured for all cluster nodes.
• Each heartbeat subnet on a node must be routed using a different physical route to another
heartbeat subnet on the other node.
• Redundant physical networks must be cabled separately between sites to maintain high
availability.
• Each subnet that is used by a package must be configured with a standby interface in the
local bridged network.
For more information on configuring cross-subnet clusters, see the Managing Serviceguard manual
available at http://www.hp.com/go/hpux-serviceguard-docs—> HP Serviceguard.
24 Metrocluster and Continentalclusters