Managing Serviceguard Extension for SAP, December 2007

Planning the Storage Layout
SAP Instance Storage Considerations
Chapter 254
Directories that Reside on Shared Disks
Volume groups on SAN shard storage are configured as part of the
SGeSAP packages. They can be either:
• instance specific or
• system specific or
• environment specific.
Instance specific volume groups are required by only one SAP instance or
one database instance. They usually get included with exactly the
package that is set up for this instance.
System specific volume groups get accessed from all instances that
belong to a particular SAP System. Environment specific volume groups
get accessed from all instances that belong to all SAP Systems installed
in the whole SAP environment. System and environment specific volume
groups are set up using HA NFS to provide access for all instances. They
shouldn’t be part of a package that is only dedicated to a single SAP
instance if there are several of them. If this package is down, then other
instances would also be impacted. As a rule of thumb, it is a good default
to put all these volume groups into a package that holds the database of
the system. For ABAP related volume groups this might be db or dbci
packages. For JAVA related volume groups this might be jdb or jdbjci
packages. Furthermore, these filesystems often provide tools for
database handling that don’t require the SAP instance at all.
In consolidated environments with more than one SAP application
component it is recommended to separate the environment specific
volume groups to a dedicated HA NFS package. This package will be
referred to as sapnfs package. It should remain running all the time,
since it is of central importance for the whole setup. Since sapnfs is just
serving networked file systems, there is rarely needed to stop this
package at any time. If environment specific volume groups become part
of a database package, there will be a potential dependency between
packages of different SAP Systems. Stopping one SAP System by halting
all related Serviceguard packages will then lead to a lack of necessary
NFS resources for otherwise unrelated SAP Systems. The sapnfs
package avoids this unpleasant dependency. It is an option to also move
the system specific volume groups to the sapnfs package. This can be
done, to keep HA NFS mechanisms completely separate.