Veritas Volume Manager 5.0 Administrator's Guide (September 2006)

78 Administering disks
Disk devices
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 “Administering dynamic multipathing (DMP)” on page 121.
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# naming format used by
the operating system. 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
■ Enclosure based naming
c#t#d# based naming
In this naming scheme, all disk devices except fabric mode disks are named using the
c#t#d# format.
The syntax of a device name is c#t#d#, where c# represents a controller on a host bus
adapter, t# is the target controller ID, and d# identifies a disk on the target controller.
Fabric mode disk devices are named as follows:
■ Disk in supported disk arrays are named using the enclosure name_# format. For
example, disks in the supported disk array name FirstFloor are named
FirstFloor_0, FirstFloor_1, FirstFloor_2 and so on. (You can use the
vxdmpadm command to administer enclosure names.)
■ Disks in the DISKS category (JBOD disks) are named using the Disk_# format.
■ Disks in the OTHER_DISKS category (disks that are not multipathed by DMP) are
named using the fabric_# format.
Enclosure based naming
Enclosure-based naming operates as follows:
■ Devices with very long device names (for example, Fibre Channel devices that
include worldwide name (WWN) identifiers) are always represented by enclosure-
based names.