Overview

Data is not information. Information is not knowledge. Knowledge is not understanding. Understanding is not wisdom.

Cliff Stoll and Gary Schubert

Every Tru64 UNIX system is different in the way its storage is configured. There are many options available. One system may be configured to use file systems to store its data, another may use raw disks, and a third might use logical volumes created by the logical storage manager (LSM). Many administrators use tape devices for their backups, while others use a newer technique known as disk-to-disk backups. Even within a relatively narrow category, such as disk-to-disk backups, there are many different technologies one could employ to obtain the desired result. A system can even be configured to use a combination of these storage options. This flexibility is powerful and gives the system administrator many tools to accomplish a given task; however, it also greatly complicates the process of troubleshooting storage in a generic way.

Our aim in this chapter is to provide the reader with a set of troubleshooting tools and techniques to aid in solving common problems seen in the storage subsystem. Because there are so many options, we cannot hope to list all the possible ways to troubleshoot storage problems. However, what at first seems like an insurmountable problem can be broken down into simpler components. Therefore, we always start a storage troubleshooting exercise by first trying to narrow the problem down to a component of the I/O subsystem, such as a disk, tape, LSM,...