Supported Configurations

Failover to an Idle Node

Figure 1-1 “Simple Failover to an Idle NFS Server” shows a simple failover from an active NFS server node to an idle NFS server node.

Figure 1-1 Simple Failover to an Idle NFS Server

Node_A is the primary node for NFS server package Pkg_1. When Node_A fails, Node_B adopts Pkg_1. This means that Node_B locally mounts the file systems associated with Pkg_1 and exports them. Both Node_A and Node_B must have access to the disks that hold the file systems for Pkg_1.

Failover between Active Nodes

Figure 1-2 “Failover from One Active NFS Server to Another” shows a failover from one active NFS server node to another active NFS server node. In Figure 1-2 “Failover from One Active NFS Server to Another”, Node_A is the primary node for Pkg_1, and Node_B is the primary node for Pkg_2. When Node_A fails, Node_B adopts Pkg_1 and becomes the server for both Pkg_1 and Pkg_2.

Figure 1-2 Failover from One Active NFS Server to Another

	NOTE: During a package failover, the NFS server may receive a status information messages such as: Input/output error, Stale NFS file handle, or Write error: Stale NFS file handle. The result is a retry. If the package fails over during a user file access, the client may experience a momentary hang. Access continues as soon as the package has completed failover to the other node.

Failover with an Adoptive Node for Multiple Packages

Figure 1-3 “A Host Configured as Adoptive Node for Multiple Packages” shows a three-node configuration where one node is the adoptive node for packages on both of the other nodes. If either Node_A or Node_C fails, Node_B adopts the NFS server package from that node. When Node_A fails, Node_B becomes the server for Pkg_1. If Node_C fails, Node_B will become the server for Pkg_2.

Figure 1-3 A Host Configured as Adoptive Node for Multiple Packages

Alternatively, you can prevent Node_B from adopting more than one package at a time by setting a package control function in the package control script. With the package control function set, Node_B may adopt the package of the first node that fails, but if the second node fails, Node_B will not adopt its package. The package control function prevents a node from becoming overloaded by adopting too many packages. If an adoptive node becomes overloaded, it can fail. Refer to “Package Control Script for pkg02” for function usage.

Cascading Failover with Multiple Adoptive Nodes

Consider a package that is configured up to three adoptive nodes. Figure 1-4 “Cascading Failover, with Three Adoptive Nodes” shows this configuration. If Node_A fails, Pkg_1 is adopted by Node_B. However, if Node_B is down, Pkg_1 is adopted by Node_C, and if Node_C is down, Pkg_1 is adopted by Node_D. The adoptive nodes are listed in the package configuration file, which was generated by using cmmakepkg -p file command (see Managing Serviceguard for Linux, Chapter 6) in the order in which they will be tried. Note that all four nodes must have access to the disks for the Pkg_1 file systems.

Figure 1-4 Cascading Failover, with Three Adoptive Nodes