Managing Serviceguard Extension for SAP on Linux (IA64 Integrity and x86_64), February 2008

Understanding Serviceguard Extension for SAP on Linux
Clustering Stand-Alone J2EE Components
Chapter 118
Highly Available (HA) NFS
Distributed SAP environments require the Network File System (NFS)
to be highly available. Serviceguard Extension for SAP on Linux
packages can be combined with the Serviceguard NFS toolkit for Linux
to achieve this functionality. Typically, the Serviceguard Extension for
SAP on Linux database package also provides Highly Available NFS
functionality.
Serviceguard Extension for SAP on Linux cluster hosts can usually act
as Highly Available NFS servers and as NFS clients that access these
server's file systems. The cross-mounting approach is taken to achieve
this. The logical volumes that contain the NFS file systems are mounted
below a specific directory, usually called /export. They are accessed via
a different path by the NFS clients that is linked to a location below
/import, which is monitored by an automounter instance that provides
the linkage between corresponding /export and /import directories.
This setup allows NFS servers to be failed to NFS client hosts without
getting into trouble with busy mount points for the disk devices. It also
avoids adding static mounts to Highly Available NFS file systems, which
also cause problems if the NFS server is not running during reboot time.
NOTE Database data files need to be treated differently to avoid measurable
performance impacts and data inconsistencies.