The Dynamic Multipathing (DMP) feature of Veritas Volume Manager (VxVM) provides greater availability, reliability and performance by using path failover and load balancing. This feature is available for multiported disk arrays from various vendors.
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 type. DMP can also differentiate between different enclosures of a supported array type that are connected to the same host system.
The multipathing policy used by DMP depends on the characteristics of the disk array.
DMP supports the following standard array types:
An array support library (ASL) 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 multipathing 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 multipathing for a disk enclosure in a SAN environment shows an example where two paths, sdf and sdm, exist to a single disk in the enclosure, but VxVM uses the single DMP node, enc0_0, to access it.