Veritas Dynamic Multi-Pathing (DMP) provides greater availability, reliability, and performance by using path failover and load balancing. This feature is available for multiported disk arrays from various vendors.
DMP coexists with the native multi-pathing in HP-UX.
See DMP coexistence with HP-UX native multi-pathing.
Multiported disk arrays can be connected to host systems through multiple paths. To detect the various paths to a disk, DMP uses a mechanism that is specific to each supported array. DMP can also differentiate between different enclosures of a supported array that are connected to the same host system.
The multi-pathing policy that is used by DMP depends on the characteristics of the disk array.
DMP supports the following standard array types:
For this release, only the A/A, A/A-A, and ALUA arrays are supported on HP-UX.
An array policy module (APM) may define array types to DMP in addition to the standard types for the arrays that it supports.
VxVM uses DMP metanodes (DMP nodes) to access disk devices connected to the system. For each disk in a supported array, DMP maps one node to the set of paths that are connected to the disk. Additionally, DMP associates the appropriate multi-pathing policy for the disk array with the node. For disks in an unsupported array, DMP maps a separate node to each path that is connected to a disk. The raw and block devices for the nodes are created in the directories /dev/vx/rdmp and /dev/vx/dmp respectively.
Figure: How DMP represents multiple physical paths to a disk as one node shows how DMP sets up a node for a disk in a supported disk array.
VxVM implements a disk device naming scheme that allows you to recognize to which array a disk belongs.
Figure: Example of multi-pathing for a disk enclosure in a SAN environment shows an example where two paths, c1t99d0 and c2t99d0, exist to a single disk in the enclosure, but VxVM uses the single DMP node, enc0_0, to access it.