20Understanding Veritas Volume Manager

How VxVM handles storage management

How VxVM handles storage management

VxVM uses two types of objects to handle storage management: physical objects and virtual objects.

■Physical objects—physical disks or other hardware with block and raw operating system device interfaces that are used to store data.

■Virtual objects—When one or more physical disks are brought under the control of VxVM, it creates virtual objects called volumes on those physical disks. Each volume records and retrieves data from one or more physical disks. Volumes are accessed by file systems, databases, or other applications in the same way that physical disks are accessed. Volumes are also composed of other virtual objects (plexes and subdisks) that are used in changing the volume configuration. Volumes and their virtual components are called virtual objects or VxVM objects.

Physical objects—physical disks

A physical disk is the basic storage device (media) where the data is ultimately stored. You can access the data on a physical disk by using a device name to locate the disk.

Figure 1-1shows 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 Dynamic Discovery Layer (DDL) and Dynamic Multipathing (DMP) features of VxVM.