Using udev to Simplify HP Serviceguard for Linux Configuration, October 2006

Executive Summary

Device names are generally assigned by Linux at boot time. Using these device names in

scripts or other applications can cause problems as configurations change over time. HP

Serviceguard for Linux requires the use of device names in user modified scripts and for

LockLUN. This white paper describes the use of the Linux function udev to provide

persistent device names with Serviceguard for Linux so that scripts are not affected by

changes in system configuration.

This white paper is not intended to replace the manpage and other udev documentation

(see the references at the end of the white paper). The intent is to highlight tools and

configuration recommendations that are known to work with HP Serviceguard for Linux.

Introduction

Configuring an HP Serviceguard for Linux cluster requires the configuration and use of

storage. When a Linux system boots, it assigns a name to each storage device it

discovers. Typically these devices have names of the form /dev/sdN or /dev/cciss/cXdY

where N is one or more letters and X, Y, and Z are numbers. In a cluster, we are most

concerned with shared storage. Since the storage arrays that are used are configurable,

these device name assignments can change if the array configuration is changed. While

there may be other actions within the system that can cause a change, the important factor

is that any name change might affect the cluster configuration. To simplify management of

the cluster, these name changes should be “hidden” from Serviceguard for Linux.

Using the “multi-path” feature of the QLogic FibreChannel driver can provide automatic

persistence. Other multipath tools may, or may not provide device name persistence.

Also, configurations that do not have multiple paths to storage, such as when the MSA500

arrays are used, can really benefit from another persistent naming mechanism. In some

cases, the Linux function udev can provide this persistent naming. The method of using

udev with Serviceguard is described here.

This whitepaper covers only RedHat 4, Novell SLES9, and Novell SLES10. These

operating systems use the “2.6” Linux kernel.

Audience

This document is for users of HP Serviceguard on Linux who are setting up a cluster or

writing package control scripts.

It is assumed that the reader has a general understanding of HP Serviceguard for Linux

and of configuring a Linux system.