Veritas Volume Manager 5.1 SP1 Administrator"s Guide (5900-1506, April 2011)

the disk. The physical disk device name varies with the computer system you use.

Not all parameters are used on all systems.

Figure 1-1 shows how a physical disk and device name (devname) are illustrated

in this document.

Figure 1-1

Physical disk example

devname

In HP-UX 11i v3, disks may be identified either by their legacy device name, which

takes the form c#t#d#, or by their persistent (or agile) device name, which takes

the form disk##.

In a legacy device name, c# specifies the controller, t# specifies the target ID, and

d# specifies the disk. For example, the device name c0t0d0 is the entire hard disk

that is connected to controller number 0 in the system, with a target ID of 0, and

physical disk number of 0. The equivalent persistent device name might be disk33.

In this document, legacy device names are generally shown as this format is the

same as the default format that is used by the Device Discovery Layer (DDL) and

Dynamic Multi-Pathing (DMP).

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.

VxVM accesses all disks as entire physical disks without partitions.

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.

Understanding Veritas Volume Manager

How VxVM handles storage management