A stretched cluster is ideal for situations
where each site is located in the same geographical location. Typically,
all nodes are on a common storage area network (SAN). At a minimum,
the active repository and any backup repositories are shared between
sites, as are any disks in resource groups that can run at either
site. Stretched clusters can support LVM cross-site mirroring, and HyperSwap®.
When you use a stretched cluster in your environment, a single Cluster Aware AIX® (CAA)
cluster is deployed across sites in the cluster.
If IP communication fails and your environment is using stretched
clusters, all nodes in the cluster can use the disk heartbeat function
to communicate and to keep your environment operational.
Stretched clusters must meet the following requirements:
Site communication can use unicast or multicast
IP addresses.
Share at least one repository disk between the sites.
The following table displays the supported stretched cluster configurations for
split policy options and merge policy options. For example, in a stretched cluster you can have a
configuration with a split policy value of None and a merge policy value of
Majority. However, you cannot have a configuration with a split policy value
of Tie-breaker and a merge policy value of Majority.
Table 1. Stretched cluster options for split and merge policies
Split policy options
Merge policy options
Majority
Tie-breaker
None
X
Tie-breaker
X
The following figure is an example of a stretched cluster that
has two sites that are in different buildings, which are geographically
close to each other in the same city and that share a repository disk. Figure 1. Typical stretched cluster configuration
