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Chapter
3
Administering dynamic
multipathing (DMP)
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.
DMP coexists with the native multipathing in HP-UX. For more information, see
“DMP coexistence with HP-UX native multipathing” on page 130.
How DMP works
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.
See “Discovering and configuring newly added disk devices” on page 82 for a
description of how to make newly added disk hardware known to a host system.
The multipathing policy used by DMP depends on the characteristics of the disk
array:
■ An Active/Passive array (A/P array) allows access to its LUNs (logical units;
real disks or virtual disks created using hardware) via the primary (active)
path on a single controller (also known as an access port or a storage
processor) during normal operation.
In implicit failover mode (or autotrespass mode), an A/P array automatically
fails over by scheduling I/O to the secondary (passive) path on a separate
controller if the primary path fails. This passive port is not used for I/O
until the active port fails. In A/P arrays, path failover can occur for a single
LUN if I/O fails on the primary path.