HP XC System Software Installation Guide Version 3.2

1.9.6 Assigning Node Roles For Improved Availability
An important part of planning your strategy for improved availability is to determine the services
for which availability is vital to the system operation. Services are delivered in node roles. A
node role is an abstraction that combines one or more services into a group and provides a
convenient way of installing services on a node.
In this release, improved availability is supported for the services listed in Table 1-2. Also listed
in the table are things to consider about the role assignments if you plan to implement improved
availability for one or more of these services.
Read Appendix F (page 209) to learn more about default role assignments and the full set of
services provided by each role.
Table 1-2 Role and Service Placement for Improved Availability
Special Considerations for Role Assignment
Service is Delivered in This
RoleService Name
The dbserver service is present on the head node by default
and cannot be moved. Thus, to achieve improved availability
of the dbserver service, the following is required:
• You must install and configure the HP StorageWorks
Scalable File Share (SFS) software, which must be purchased
separately from HP.
When improved availability is enabled, the database tables
are moved to the system-wide /hptc_cluster file system
(rather than the default location in the /var/lib/mysql
directory). In order for /hptc_cluster to be highly
available, it must reside on an SFS server.
• You must configure the head node into an availability set
with one additional node.
• You must assign the avail_node_management role to
the additional node.
For more information about the avail_node_management
role, see “Avail_node_management Role” (page 211).
avail_node_management
Database server
(dbserver)
The login role supplies the LVS director service. LVS requires
the login role on three nodes to attain improved availability:
• One node which is always a real server
• A pair of nodes to act as the LVS director and a backup for
the LVS director associated into an availability set. The LVS
director also acts as a real server; the backup never does.
This means that to have n real servers during normal operation,
you assign the login role to n+1 nodes because the backup for
the LVS director is never a real server, but it must have a
login role to act as a backup. When failover occurs, the
backup takes over the director role, but it does not become a
real server. This means that when the LVS director service is
failed over, there is one less real server available (temporarily)
because the director, which was a real server, is unavailable.
login
Linux Virtual Server
(LVS) director
32 Preparing for a New Installation