Managing Serviceguard Fifteenth Edition, reprinted May 2008

Understanding Serviceguard Software Components
Volume Managers for Data Storage
Chapter 3112
Volume Managers for Data Storage
A volume manager is a tool that lets you create units of disk storage
known as storage groups. Storage groups contain logical volumes for use
on single systems and in high availability clusters. In Serviceguard
clusters, storage groups are activated by package control scripts.
Types of Redundant Storage
In Serviceguard, there are two types of supported shared data storage:
mirrored individual disks (also known as JBODs, for “just a bunch of
disks”), and external disk arrays which configure redundant storage in
hardware. Two types of mirroring are RAID1 and RAID5. Here are some
differences between the two storage methods:
• If you are using JBODs, the basic element of storage is an individual
disk. This disk must be paired with another disk to create a mirror
(RAID1). (Serviceguard configurations usually have separate mirrors
on different storage devices).
• If you have a disk array, the basic element of storage is a LUN, which
already provides storage redundancy via hardware RAID1 or RAID5.
About Device File Names (Device Special Files)
HP-UX releases up to and including 11i v2 use a naming convention for
device files that encodes their hardware path. For example, a device file
named /dev/dsk/c3t15d0 would indicate SCSI controller instance 3,
SCSI target 15, and SCSI LUN 0. HP-UX 11i v3 introduces a new
nomenclature for device files, known as agile addressing (sometimes
also called persistent LUN binding).
Under the agile addressing convention, the hardware path name is no
longer encoded in a storage device’s name; instead, each device file name
reflects a unique instance number, for example /dev/[r]disk/disk3,
that does not need to change when the hardware path does.
Agile addressing is the default on new 11i v3 installations, but the I/O
subsystem still recognizes the pre-11.i v3 nomenclature. This means that
you are not required to convert to agile addressing when you upgrade to
11i v3, though you should seriously consider its advantages.