HP-UX SNAplus2 R7 Administration Guide

Appendix DUsing SNAplus2 in a High Availability Environment
Figure D–2 LU Pools
Client Client Client Client
3xxx
Communications
Controller
S800
Server
IBM
Host
LAN
S800
Server
LU Pool A
The LU pool gives you the ability to add a logical layer on top of the two servers. Clients access the SNA network
by referring to the LU pool name, not to a specific LU in the pool. Within the SNAplus2 configuration above, the
LU pool contains LUs associated with two LSs — one for each S800 server. SNAplus2 automatically allocates
an available LU from the pool when you request it. In this way, high availability is built into the network with
redundant ports. If one port fails, or if one of the servers fail, SNAplus2 will continue to function through the other
server.
D.2.2 Client/Server Configuration
SNAplus2 can be configured in either a standalone or client/server configuration. The standalone configuration
requires SNAplus2 applications to run on the same system that has the SNAplus2 Link installed. The client/server
configuration provides an important benefit for high availability environments in that applications running on client
systems can access ports on multiple servers. By providing applications with multiple paths to the remote SNA
system, the client/server configuration greatly reduces the number of single points of failure.
When an SNAplus2 application starts in a client/server configuration, it tries to locate a suitable LU that is available.
It queries all of the servers that are active to see if one of them can provide an LU that has been configured to be
used by the application. If one of the servers provides a suitable LU, an LU-LU session is established between the
server and the remote SNA system. The SNAplus2 application can then access that LU-LU session. It is important
to note that the SNAplus2 application does not specify which of the active servers should provide the LU. It is
possible that more than one server can be configured to provide a suitable LU.
There are two ways that more than one server can provide a suitable LU to an SNAplus2 application running on
a client system. First, the application can be configured to use multiple LUs, and those LUs can be spread across
multiple HP 9000 servers. If the first LU is unavailable, the application can request a different one. LU pools, if
they contain LUs that use multiple SNAplus2 LSs, can be used in this fashion. Similarly, APPC transaction pro-
grams can be developed that access several local LUs that are spread across multiple HP 9000 servers. Using this
technique, SNAplus2 applications can be given access to multiple paths to the remote SNA system.
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