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10.2. Additional Configuration Considerations

In addition to the locking considerations, you should take the following into account when configuring an NFS service over a GFS or GFS2 file system.
  • Red Hat supports only Red Hat Cluster Suite configurations using NFSv3 with locking in an active/passive configuration with the following characteristics:
    • The backend file system is a GFS or GFS2 file system running on a 2 to 16 node cluster.
    • An NFSv3 server is defined as a service exporting the entire GFS/GFS2 file system from a single cluster node at a time.
    • The NFS server can fail over from one cluster node to another (active/passive configuration).
    • No access to the GFS/GFS2 file system is allowed except through the NFS server. This includes both local GFS/GFS2 file system access as well as access through Samba or Clustered Samba.
    • The GFS or GFS2 file system must be mounted with the localflocks option.
    • There is no NFS quota support on the system.
    This configuration provides HA for the file system and reduces system downtime since a failed node does not result in the requirement to execute the fsck command when failing the NFS server from one node to another.
  • The fsid= NFS option is mandatory for NFS exports of GFS/GFS2.
  • There is currently an issue with failover and failback when using NFSv3 over GFS with TCP 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/GFS2 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.
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