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When performing disk administration, it is important to understand the difference between a disk name and a device name.
The disk name (also known as a disk media name) is the symbolic name assigned to a VM disk. When you place a disk under VxVM control, a VM disk is assigned to it. The disk name is used to refer to the VM disk for the purposes of administration. A disk name can be up to 31 characters long. When you add a disk to a disk group, you can assign a disk name or allow VxVM to assign a disk name. The default disk name is diskgroup## where diskgroup is the name of the disk group to which the 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 the name of a disk device as it is known to the operating system.
Such devices are usually, but not always, located in the /dev directory. Devices that are specific to hardware from certain vendors may use their own path name conventions.
VxVM supports the disk partitioning scheme provided by the operating system. The syntax of a device name is hdx[N] or sdx[N], where x is a letter that indicates the order of EIDE (hd) or SCSI (sd) disks seen by the operating system, and N is an optional partition number in the range 1 through 15. An example of a device name is sda7, which references partition 7 on the first SCSI disk. If the partition number is omitted, the device name indicates the entire disk.
Devices that are specific to hardware from certain vendors may have different path names. For example, the COMPAQ SMART and SMARTII controllers use device names of the form /dev/ida/cXdXpX and /dev/cciss/cXdXpX.
VxVM uses the device names to create 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 one or more physical paths, perhaps 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 that are subsumed by a DMP metadevice, and to display the status of each path (for example, whether it is enabled or disabled).