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

Planning a File System Layout for SAP in a Serviceguard/LX Cluster Environment
About Impacted File Systems
Chapter 250
NOTE In prior SGeSAP/LX documentation this category (LOCAL) was called
“Environment specific”.
SHARED NFS or SHARED EXCLUSIVE
SHARED NFS
In this category file system data is shared among the SAP instances via
NFS and is made available / exported to all cluster nodes. An example
could be /sapmnt/<SID>/profile directory which contains the profile
for all SAP instances in the cluster. Each cluster mounts this directory as
an NFS client.
One of the cluster node will also be the NFS server of these directories.
This node will have both the NFS client and the NFS server mounts
active at the same time. This is sometimes called a NFS loopback mount.
Should this cluster node fail, then the NFS exported directories will be
relocated to another cluster node and will be NFS served from this node.
An advantage of an NFS shared mount is that any changes or updates to
an NFS file system contents are available instantaneously to all cluster
nodes. Compared to a LOCAL mount point and where the file systems
have to be kept in sync cluster wide with local copies this option doesn’t
have this administration overhead.
A limiting factor could be that NFS mounted file systems will not provide
the same level of IO performance a LOCAL mounted file system. Many of
the above listed SAP file systems though are more of STATIC nature in
their IO behavior so therefore should not cause an I/O limitation. If high
I/O is required then the SHARED EXCLUSIVE mount should be used.
NOTE In prior SGeSAP/LX documentation this category was called “System
specific.”