Specifications

NFS Client Mounting Considerations
NFS Client Mounting Considerations
An NFS Server provides a network-based storage system to client computers. To utilize this
resource, the client systems must “mount” the file systems that have been NFS exported by the NFS
server. There are several options that system administrators must consider on how NFS clients are
connected to the LifeKeeper protected NFS resources.
UDP or TCP?
The NFS Protocol can utilize either the User Datagram Protocol (UDP) or the Transmission Control
Protocol (TCP). NFS has historically used the UDP protocol for client-server communication. One
reason for this is that it is easier for NFS to work in a stateless fashion using the UDP protocol. This
“statelessness” is valuable in a high availability clustering environment, as it permits easy
reconnection of clients if the protected NFS server resource is switched between cluster hosts. In
general, when working with a LifeKeeper protected NFS resource, the UDP protocol tends to work
better than TCP.
Sync Option in /etc/exports
Specifying “sync” as an export option is recommended for LifeKeeper protected NFS resources. The
“sync” option tells NFS to commit writes to the disk before sending an acknowledgment back to the
NFS client. The contrasting “async” option is also available, but using this option can lead to data
corruption, as the NFS server will acknowledge NFS writes to the client before committing them to
disk. NFS clients can also specify “sync” as an option when they mount the NFS file system.
Red Hat EL6 (and Fedora 14) Clients with Red Hat EL6 NFS Server
Due to what appears to be a bug in the NFS server for Red Hat EL6, NFS clients running Red Hat
EL6 (and Fedora 14) cannot specify both an NFS version (nfsvers) and UDP in the mount command.
This same behavior has been observed on an Ubuntu10.10 client as well. This behavior is not seen
with Red Hat EL5 clients when using a Red Hat EL6 NFS server, and it is also not seen with any
clients using a Red Hat EL5 NFS server. The best combination of NFS mount directives to use with
Red Hat EL6 (Fedora 14) clients and a Red Hat EL 6 NFS server is:
mount <protected-IP>:<export> <mount point>
-onfsvers=2,sync,hard,intr,timeo=1
l This combination produces the fastest re-connection times for the client in case of a
switchover or failover of the LifeKeeper protected NFS server.
Red Hat EL5 NFS Clients with a Red Hat EL6 NFS Server
The best combination of options when using NFS clients running Red Hat EL5 with a Red Hat EL6
NFS server for fast reconnection times is:
mount <protected-IP>:<export> <mount point>
-onfsvers=3,sync,hard,intr,timeo=1,udp
Cluster Example
Expanded Multicluster Example
218User Guide