Configuration Considerations - Red Hat ENTERPRISE LINUX 5 - CONFIGURATION NFS OVER GFS Configuration Manual

Chapter 9.

Configuration Considerations

When configuring an NFS service over a GFS file system, you may want to take the following into
account.
• Do not use NFS locks in a failover situation such as the one described in this configuration, as this
may cause a duplicate lock situation. The GFS file system correctly distributes the locks between
nodes.
• The Linux NFS server as used in Red Hat Enterprise Linux 5 is not cluster aware. NFS state
information is held on a per machine basis and there is a slight but definite chance of file corruption
should two NFS servers try to write to the same file at the same time, even in a GFS environment.
Because of this the current recommendation is to only export any given file system on one NFS
machine only.
• There is currently an issue with failover and failback when using NFSv3 over GFS when the
following scenario comes into play:
1. Client A mounts from server 1.
2. The system administrator moves NFS service from server 1 to server 2.
3. The client resumes I/O operations.
4. The system administrator moves NFS service from server 2 to server 1.
In this situation, the NFS service on server 1 does not get shut down because this would render
other NFS services inoperable.
Should this situation arise, you should move all NFS services off of server 1 and run the service
nfs restart. After this you can safely migrate your NFS services back to server 1.
• If problems arise with your cluster (for example, the cluster becomes inquorate and fencing is not
successful), the clustered logical volumes and the GFS file system will be frozen and no access is
possible until the cluster is quorate. You should consider this possibility when determining whether
a simple failover solution such as the one defined in this procedure is the most appropriate for your
system.
• With GFS file systems, you can perform a backup on the data from a second node that is not
actively providing the service to decrease the load of the active node. This may prove useful when
using a backup mechanism where the system load is sometimes very high.
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