Technical white paper Using NFS as a file system type with HP Serviceguard A.11.
Introduction This white paper explains how to configure packages that need access to an NFS-imported file system as shared storage. This capability is available as of HP Serviceguard version A.11.20. In previous releases, Serviceguard has supported only direct-attached storage, using technologies such as SCSI, Fibre Channel, or SAS. Note: Although HP Serviceguard A.11.20 supports NFS-imported storage, direct attached storage is still recommended over NFS for performance reasons.
• The NFS server itself should be highly available. The specific configuration will depend on the server platform being used. It is possible to have the package that uses the NFS file system as shared storage and the package that provides the NFS file system running in the same cluster. In such a configuration, the NFS client package must not depend on the NFS server package. If the NFS server package fails over, the client package need not be failed over.
Configuring the cluster parameter CONFIGURED_IO_TIMEOUT_EXTENSION In a Serviceguard cluster in which NFS-imported file systems are used, an unlikely but possible scenario exists in which data corruption could occur. The scenario is as follows: 1. 2. 3. 4. 5. A Serviceguard package using an NFS file system (“NFSPkg”) is running on cluster node client-1 Node client-1 issues an NFS write request immediately before NFSPkg moves to another cluster node.
In the example in figure 1, with only one switch between the NFS server and the NFS client set the CONFIGURED_IO_TIMEOUT_EXTENSION to the MBTD value of the switch in microseconds. In this case, if the MBTD of the switch is one second, set the CONFIGURED_IO_TIMEOUT_EXTENSION to 1000000. Figure 1.
If there is more than one switch between the NFS server and the Serviceguard nodes, set CONFIGURED_IO_TIMEOUT_EXTENSION to the sum of the MBTD values for each of the switches in the path (remember to use microseconds). In the example in figure 2, with two switches between the NFS server and the NFS client, set the CONFIGURED_IO_TIMEOUT_EXTENSION to the sum of all switches MBTD value in microseconds, which in this case is 1+1 = 2 seconds; so set CONFIGURED_IO_TIMEOUT_EXTENSION to 2000000. Figure 2.
In the example in figure 3, there are multiple routes or paths between the NFS server and the NFS client, and the packet can travel by any path. Configure CONFIGURED_IO_TIMEOUT_EXTENSION to sum of the MBTD values in the longest route. Figure 3. The NFS client and the NFS server use more than one route to communicate When the NFS client writes packets from the NFS client to the NFS server, the data might travel through switch 1 and 2, or instead go through switch 3 and reach the NFS server.
Creating a sample NFS package You can use Serviceguard Manager to create Serviceguard packages. If you decide instead to use Serviceguard commands to create packages, follow these steps to create a package that uses NFS-imported storage. • Before you start: Verify that the cluster configuration adheres to the recommendations and guidelines in this white paper.
– Step 6: Apply the package configuration file. truck:/>cmapplyconf -v -P pkg.ascii Begin package verification... Checking existing configuration ... Done Attempting to add package NFSPkg. Validating package NFSPkg via /etc/cmcluster/scripts/mscripts/master_control_script.sh ... Waiting for up to 1200 seconds for the validation. Validation for package NFSPkg succeeded via /etc/cmcluster/scripts/mscripts/master_control_script.sh. Maximum configured packages parameter is 300. Configuring 1 package(s).
Sample cmviewcl line output The cmviewcl line output is enhanced to display the NFS server. truck:/>cmviewcl –v –fline -p NFSPkg ...
For more information To learn more, please visit: HP Serviceguard Solutions for HP-UX 11i: hp.com/go/serviceguardsolutions For technical documentation: • HP Serviceguard Solutions for HP-UX 11i: hp.com/go/hpux-serviceguard-docs • HP Serviceguard Solutions for Linux: hp.com/go/linux-serviceguard-docs • Managing Serviceguard Manual: hp.com/go/hpux-serviceguard-docs HP Serviceguard User Guide • Managing Serviceguard Manual: hp.
