VERITAS Volume Manager 3.1 Administrator's Guide

Volume Manager Operations
Dynamic Multipathing (DMP)
Chapter 3122
Dynamic Multipathing (DMP)
NOTE You may need an additional license to use this feature.
On some systems, the Volume Manager supports multiported disk
arrays. It automatically recognizes multiple I/O paths to a particular
disk device within the disk array. The Dynamic Multipathing feature of
the Volume Manager provides greater reliability by providing a path
failover mechanism. In the event of a loss of one connection to a disk, the
system continues to access the critical data over the other sound
connections to the disk. DMP also provides greater I/O throughput by
balancing the I/O load uniformly across multiple I/O paths to the disk
device.
In the Volume Manager, all the physical disks connected to the system
are represented as metadevices with one or more physical access paths.
A single physical disk connected to the system is represented by a
metadevice with one path. A disk that is part of a disk array is
represented by a metadevice that has two physical access paths. You can
use the Volume Manager administrative utilities such as the vxdisk
utility to display all the paths of a metadevice and status information of
the various paths.
Path Failover Mechanism
DMP enhances system reliability when used with multiported disk
arrays. In the event of the loss of one connection to the disk array, DMP
automatically selects the next I/O paths for the I/O requests dynamically
without action from the administrator.
DMP allows the administrator to indicate to the DMP subsystem in the
Volume Manager whether the connection is repaired or restored. This is
called DMP reconfiguration.The reconfiguration procedure also allows
the detection of newly added devices, as well as devices that are removed
after the system is fully booted (if the operating system detects them
properly).