Expand Configuration and Management Manual (G06.24+)

Planning for ServerNet Clusters
Expand Configuration and Management Manual—523347-008
4-8
Examples of ServerNet Clusters Coexisting With
ATM or IP
for inter-ServerNet cluster communications without line hops, add ATM or IP
connections within the ServerNet cluster as well.
In Figure 4-3, note that the multiple inter-ServerNet cluster of ATM connections or IP
connections produces a fault-tolerant design.
ServerNet Clusters Connected By a Single ATM or IP Line
(Not Recommended)
All the systems in Figure 4-4 are NonStop S-series systems.
This topology is not recommended as a solution for enabling communication between
two ServerNet clusters due to higher processor use, traffic bottlenecks, and a lack of
overall network fault tolerance.
Processor use is higher whenever traffic flows between the two ServerNet clusters due
to a technology change between \HHH and \DDD which causes the Expand line
handlers to be used at every node on the route (including the source and destination
nodes). For example, when \GGG requests information from \CCC, six Expand line
handlers are invoked: one in \GGG, two in \DDD, two in \HHH, and one in \CCC.
Line-handler passthrough traffic uses at least twice as much processor time as does
direct traffic. Traffic bottlenecks can occur at \HHH and \DDD when numerous requests
for information are made by systems located on separate ServerNet clusters. Overall
network fault tolerance is not preserved. If \HHH or \DDD becomes unavailable, the
two ServerNet clusters are isolated from each other.
Figure 4-3. ServerNet Clusters Connected by ATM or IP Lines
\BBB #2
Cluster
Switch
\AAA #1
\GGG #9\CCC #3
Cluster
Switch
\DDD #7
\EEE #5\FFF #4
\HHH #6
\JJJ #8
5-Node ServerNet Cluster 4-Node ServerNet Cluster
ATM or IP
ATM
or IP
ATM or IP
ATM or IP
VST062