The database and the SAP R/3 central instance are always running
on nodes that are protected by MC/ServiceGuard. This is different
for systems that have the enqueue service, SAP R/3's central
lock handling server process, protected by HP Somersault (B8438). Refer
to “SGeSAP and HP Somersault” for additional information.
Other SAP R/3 services can be run on HP-UX application server
hosts. These hosts do not need to be part of the MC/ServiceGuard cluster.
Even if the additional SAP R/3 services are run on nodes in the MC/ServiceGuard cluster,
they are not protected by MC/ServiceGuard. A combination of Windows
NT/HP-UX application servers is technically possible but additional
software is required to access HP-UX filesystems or HP-UX-like remote
shells from the Windows NT system.
All application servers different from the central instance
are called additional application servers.
An additional application server that runs on a cluster node is
called an internal application server. External application
servers run on HP-UX- or Windows NT-hosts that are not part of the
cluster. Even if application servers are external to the cluster, they
are affected by package startup and shutdown.
Run the SAP R/3 services dialog, update, batch, spool, and
gateway, on additional application servers. Do not run the message
or enqueue services on additional application servers. Set up one
message server and one enqueue server for each SAP R/3 system.
The message server, enqueue server, database and NFS server
are all single points of failure (SPOF). To maintain high availability,
all these SPOFs for the SAP R/3 system must be eliminated by configuring
them in MC/ServiceGuard cluster nodes.
In standard SAP R/3 scenarios the SPOFs database, NFS, message
and enqueue server are all protected. It is highly recommended that
you also protect at least one instance of each additional SAP R/3 service
in the MC/ServiceGuard cluster.
For all application server nodes outside the MC/ServiceGuard cluster, consider
the following for each of the SAP R/3 services:
Dialog—Logon using saplogon for an application server groups instead of saptemu/sapgui for each individual application server. When logging
on to an application server group with two or more application servers,
you not need a different login procedure even if one of the application
servers of the group fails. Also, using login groups provides workload
balancing between application servers.
Update—Configure an update service on a node
only for application services running on the same node. This ensures
that the remaining SAP R/3 servers, running on different nodes,
are affected if an outage occurs on the update server. However,
if the update server is configured to be responsible for application
servers running on different nodes, any failure of the update server
will lead to subsequent outages at these nodes. Configuring the
update service on the high available central instance is recommended.
Consider using local update servers only if performance issues require
it.
Batch—Do not specify a destination
host when defining a batch job. This allows the batch
scheduler to choose a batch server that is available at the start
time of the batch job. If you must specify a destination host, specify
the batch server running on the highly available central instance.
Spool—Print requests stay in the system until
the node is available again and the spool server has been restarted.
These requests could be moved manually to other spool servers if
one spool server is unavailable for a long period of time. An alternative
is to print all time critical documents through the highly available
spool server of the central instance.
Gateway—You don't have to worry about the gateway
processes gwrd and gwwr with SAP R/3 3.0 or higher. Do not confuse this with
the SNA gateway.
SGeSAP monitors the hardware within the cluster (CPU, Network
cards, etc), but it does not monitor the health of the SAP R/3 processes
or the database. This means that MC/ServiceGuard will not switch
the packages to another node if you have problems with SAP R/3 or
the database.
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