VERITAS Volume Manager 4.1 Administrator's Guide

Administering Disks
Disk Devices
Chapter 264
Disk Devices
When performing disk administration, it is important to understand the difference between a
disk name and a device name.
When a disk is placed under VxVM control, a VM disk is assigned to it. You can define a
symbolic disk name (also known as a disk media name) to refer to a VM disk for the purposes
of administration. A disk name can be up to 31 characters long. If you do not assign a disk
name, it defaults to diskgroup## where diskgroup is the name of the disk group to which
disk is being added and ## is a sequence number. Your system may use device names that
differ from those given in the examples.
The device name (sometimes referred to as devname or disk access name) defines where the
disk is located in a system. Such devices are usually, but not always, located in the
/dev/[r]dsk directories. Devices that are specific to hardware from certain vendors may have
different path names.
VxVM recreates disk devices, including those from the /dev/[r]dsk directories, as
metadevices in the /dev/vx/[r]dmp directories. The dynamic multipathing (DMP) feature of
VxVM uses these metadevices (or DMP nodes) to represent disks that can be accessed by more
than one physical path, usually via different controllers. The number of access paths that are
available depends on whether the disk is a single disk, or is part of a multiported disk array
that is connected to a system.
You can use the vxdisk utility to display the paths subsumed by a metadevice, and to display
the status of each path (for example, whether it is enabled or disabled). For more information,
see Chapter 3, “Administering Dynamic Multipathing (DMP),” on page 109. Device names
may also be remapped as enclosure-based names as described in the following section.
Disk Device Naming in VxVM
Prior to VxVM 3.2, all disks were named according to the c#t#d# format. Fabric mode disks
were not supported by VxVM. From VxVM 3.2 onward, there are two different methods of
naming disk devices:
• c#t#d# Based Naming Scheme
• Enclosure Based Naming Scheme
c#t#d# Based Naming Scheme
In this naming scheme, all disk devices except fabric mode disks are named using the c#t#d#
format.