Novell LINUX ENTERPRISE 11 - HIGH AVAILABILITY, Manual, Page: 18 / 298

back (move back) to Web Server 1, or they can stay where they are. This is dependent
on how you configured the resources for them. Migrating the services back to Web
Server 1 will incur some down-time, so the High Availability Extension also allows
you to defer the migration until a period when it will cause little or no service interrup-
tion. There are advantages and disadvantages to both alternatives.
The High Availability Extension also provides resource migration capabilities. You
can move applications, Web sites, etc. to other servers in your cluster as required for
system management.
For example, you could have manually moved Web Site A or Web Site B from Web
Server 1 to either of the other servers in the cluster. You might want to do this to upgrade
or perform scheduled maintenance on Web Server 1, or just to increase performance
or accessibility of the Web sites.
1.3 Cluster Configurations
Cluster configurations with the High Availability Extension might or might not include
a shared disk subsystem. The shared disk subsystem can be connected via high-speed
Fibre Channel cards, cables, and switches, or it can be configured to use iSCSI. If a
server fails, another designated server in the cluster automatically mounts the shared
disk directories that were previously mounted on the failed server. This gives network
users continuous access to the directories on the shared disk subsystem.
IMPORTANT: Shared Disk Subsystem with cLVM
When using a shared disk subsystem with cLVM, that subsystem must be con-
nected to all servers in the cluster from which it needs to be accessed.
Typical resources might include data, applications, and services. The following figure
shows how a typical Fibre Channel cluster configuration might look.
8 High Availability Guide