Managing Serviceguard Eighteenth Edition, September 2010
The following rules and restrictions apply.
• NFS mounts are supported only for modular, failover packages.
See Chapter 6 (page 279) for a discussion of types of packages.
• So that Serviceguard can ensure that all I/O from a node on which a package has
failed is flushed before the package restarts on an adoptive node, all the network
switches and routers between the NFS server and client must support a worst-case
timeout, after which packets and frames are dropped. This timeout is known as
the Maximum Bridge Transit Delay (MBTD).
IMPORTANT: Find out the MBTD value for each affected router and switch from
the vendors' documentation; determine all of the possible paths; find the worst
case sum of the MBTD values on these paths; and use the resulting value to set
the Serviceguard CONFIGURED_IO_TIMEOUT_EXTENSION parameter. For
instructions, see the discussion of this parameter under “Cluster Configuration
Parameters ” (page 143).
Switches and routers that do not support MBTD value must not be used in a
Serviceguard NFS configuration. This might lead to delayed packets that in turn
could lead to data corruption.
• Networking among the Serviceguard nodes must be configured in such a way that
a single failure in the network does not cause a package failure.
• Only NFS client-side locks (local locks) are supported.
Server-side locks are not supported.
• Because exclusive activation is not available for NFS-imported file systems, you
should take the following precautions to ensure that data is not accidentally
overwritten.
— The server should be configured so that only the cluster nodes have access to
the file system.
— The NFS file system used by a package must not be imported by any other
system, including other nodes in the cluster.
— The nodes should not mount the file system on boot; it should be mounted
only as part of the startup for the package that uses it.
— The NFS file system should be used by only one package.
— While the package is running, the file system should be used exclusively by
the package.
— If the package fails, do not attempt to restart it manually until you have verified
that the file system has been unmounted properly.
Package Configuration Planning 175