VERITAS Volume Manager 4.1 Administrator's Guide

Understanding VERITAS Volume Manager
How VxVM Handles Storage Management
Chapter 1 5
The figure, “Physical Disk Example,” shows how a physical disk and
device name (devname) are illustrated in this document. For example,
device name c0t0d0 is the entire hard disk connected to controller
number 0 in the system, with a target ID of 0, and physical disk number
0.
Figure 1-1 Physical Disk Example
VxVM writes identification information on physical disks under VxVM
control (VM disks). VxVM disks can be identified even after physical disk
disconnection or system outages. VxVM can then re-form disk groups
and logical objects to provide failure detection and to speed system
recovery.
For HP-UX 11.x, all the disks are treated and accessed by VxVM as
entire physical disks using a device name such as c#t#d#.
Disk Arrays
Performing I/O to disks is a relatively slow process because disks are
physical devices that require time to move the heads to the correct
position on the disk before reading or writing. If all of the read or write
operations are done to individual disks, one at a time, the read-write
time can become unmanageable. Performing these operations on
multiple disks can help to reduce this problem.
A disk array is a collection of physical disks that VxVM can represent to
the operating system as one or more virtual disks or volumes. The
volumes created by VxVM look and act to the operating system like
physical disks. Applications that interact with volumes should work in
the same way as with physical disks.
Figure 1-2 illustrates how VxVM represents the disks in a disk array as
several volumes to the operating system.
devname