Novell BUSINESS CONTINUITY CLUSTERING 1.2.1 - ADMINISTRATION Administration Manual page 16

At least one storage system must reside in each data center. The data is replicated between locations
by using host-based mirroring or storage-based mirroring. For information about using mirroring
solutions for data replication, see
on page 14. Link latency can occur between nodes at different sites, so the heartbeat tolerance
between nodes of the cluster must be increased to allow for the delay.
The split-brain detector (SBD) is mirrored between the sites. Failure of the site interconnect can
result in LUNs becoming primary at both locations (split brain problem) if host-based mirroring is
used.
In the stretch-cluster architecture shown in
that are geographically separated. The server nodes in both data centers are part of one cluster, so
that if a disaster occurs in one data center, the nodes in the other data center automatically take over.
Figure 1-1
Server 1
Fibre Channel
Switch
Cluster of Clusters
A cluster of clusters consists of multiple clusters in which each cluster is located in a geographically
separate data center. Each cluster can be in different Organizational Unit (OU) containers in the
same eDirectory tree, or in different eDirectory trees. Each cluster can be in a different IP subnet.
A cluster of clusters provides the ability to fail over selected cluster resources or all cluster resources
from one cluster to another cluster. For example, the cluster resources in one cluster can fail over to
separate clusters by using a multiple-site fan-out failover approach. A given service can be provided
by multiple clusters. Resource configurations are replicated to each peer cluster and synchronized
manually. Failover between clusters requires manual management of the storage systems and the
cluster.
16 BCC 1.2.1: Administration Guide for OES 2 SP2 Linux
Section 1.2.2, "Host-Based versus Storage-Based Data Mirroring,"
Stretch Cluster
Building A
Ethernet Switch
Server 2 Server 3 Server 4
Fibre Channel
Disk Array
Site 1
Figure 1-1, the data is mirrored between two data centers
8-node cluster stretched
between two sites
WAN
Cluster
Heartbeat
Server 5
SAN
Disk blocks
Building B
Ethernet Switch
Server 6 Server 7 Server 8
Fibre Channel
Switch
Fibre Channel
Disk Array
Site 2