Managing Serviceguard 12th Edition, March 2006

Understanding Serviceguard Software Components
Volume Managers for Data Storage
Chapter 3 113
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.
Examples of Mirrored Storage
Figure 3-20 shows an illustration of mirrored storage using HA storage
racks. In the example, node1 and node2 are cabled in a parallel
configuration, each with redundant paths to two shared storage devices.
Each of two nodes also has two (non-shared) internal disks which are
used for the root file system, swap etc. Each shared storage unit has
three disks, The device file names of the three disks on one of the two
storage units are c0t0d0, c0t1d0, and c0t2d0. On the other, they are
c1t0d0, c1t1d0, and c1t2d0.