78Administering disks

Disk devices

and /dev/rdisk directories. To maintain backward compatibility, HP-UX also creates legacy devices in the /dev/dsk and /dev/rdsk directories.

VxVM recreates disk devices for all paths in the operating system’s hardware device tree as metadevices (DMP nodes) in the /dev/vx/dmp and /dev/vx/rdmp directories. The dynamic multipathing (DMP) feature of VxVM uses a DMP node to represent a disk 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. DMP nodes are not used by the native multipathing feature of HP-UX.

If a legacy device special file does not exist for the path to a LUN, DMP generates the DMP subpath name using the c#t#d# format, where the controller number in c# is set to 512 plus the instance number of the target path to which the LUN path belongs, the target is set to t0, and the device number in d# is set to the instance number of the LUN path. As the controller number is greater than 512, DMP subpath names that are generated in this way do not conflict with any legacy device names provided by the operating system. If a DMP subpath name has a controller number that is greater than 512, this implies that the operating system does not provide a legacy device special file for the device.

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).

For more information, see “Administering dynamic multipathing (DMP)” on page 125.

Device names may also be remapped as enclosure-based names as described in the following section.

Disk device naming in VxVMThere are two different methods of naming disk devices:■Operating system-based naming■Enclosure-based namingOperating system-based naming

Under operating system-based naming, all disk devices except fabric mode disks are displayed either using the legacy c#t#d# format or the persistent disk## format. By default, VxVM commands display the names of these devices in the legacy format as these correspond to the names of the metanodes that are created by DMP.