Veritas Volume Manager 4.1 Administrator's Guide (HP-UX 11i v3, February 2007)

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Administering Dynamic Multipathing (DMP)

Note You need a full license to use this feature.

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. See

the VERITAS Volume Manager Hardware Notes for information about supported disk

arrays.

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 63 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.

For Active/Passive arrays with LUN group failover (A/PG arrays), a group of LUNs that

are connected through a controller is treated as a single failover entity. Unlike A/P

arrays, failover occurs at the controller level, and not for individual LUNs. The

primary and secondary controller are each connected to a separate group of LUNs. If

a single LUN in the primary controller’s LUN group fails, all LUNs in that group fail

over to the secondary controller.