Veritas Volume Manager 5.0.1 Administrator's Guide, HP-UX 11i v3, First Edition, November 2009

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 81.
The multipathing policy used by DMP depends on the characteristics of the disk
array.
DMP supports the following standard array types:
Allows several paths to be used concurrently for
I/O. Such arrays allow DMP to provide greater I/O
throughput by balancing the I/O load uniformly
across the multiple paths to the LUNs. In the
event that one path fails, DMP automatically
routes I/O over the other available paths.
Active/Active (A/A)
A/A-A or Asymmetric Active/Active arrays can
be accessed through secondary storage paths with
little performance degradation. Usually an A/A-A
array behaves like an A/P array rather than an
A/A array. However, during failover, an A/A-A
array behaves like an A/A array.
Asymmetric Active/Active (A/A-A)
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.
Active/Passive (A/P)
The appropriate command must be issued to the
array to make the LUNs fail over to the secondary
path.
Active/Passive in explicit failover mode
or non-autotrespass mode (A/P-F)
Administering Dynamic Multipathing
How DMP works
138