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
SHARED NFS: the NFS automounter
Chapter 262
SHARED NFS: the NFS automounter
The option for SHARED NFS is to use the NFS automounter as
described below.
The automount scheme means that with the access to a automounter
mount point the NFS file system will be mounted to the local file system
tree for as long as it is needed. When there is no activity on that file
system the automounter will automatically unmount the file system. A
static NFS mount is usually mounted at boot time, or done manually
after boot, and only unmounted during shutdown, or by hand using the
umount command.
To configure the NFS automounter the file system /usr/sap/trans will
again be used as an example. The goal is to access /usr/sap/trans
transparently from all cluster nodes. The initial approach for configuring
the automounter on Linux:
1. As in the static NFS case from above: On the cluster node acting as
the NFS server the /usr/sap/trans volumes is mounted under an
/export directory and exported to the NFS clients. Enable a virtual
host (nfsvip) from where the NFS clients can mount file systems.
The virtual host has the advantage to it is always enabled on the
cluster node where the NFS directories are being exported from and
the NFS clients only have to mount from this name.
2. On the NFS clients (regardless if cluster node or remote system) auto
mount the NFS directories under an /import directory. The /import
directory will be used as a pseudo mountpoint because Linux does
not yet support direct map mount points when a parent mount point
exists. For example, if the automounter map /usr/sap/trans
nfsvip:/export/usr/sap/trans is used it will fail since target
directory /usr of /usr/sap/trans exists on a Linux system. This is
because the Linux automounter wants to remove any files in target
directory /usr before executing. So since we are using the
automounter Linux the only way it will work is to use a pseudo
mountpoint and create symbolic links from SAP directories pointing
to the pseudo mount points. The /import directory will just serve as
dummy place holder.