VERITAS Volume Manager 3.5 Administrator's Guide (September 2004)

Administering Dynamic Multipathing (DMP)
Enabling and Disabling Input/Output (I/O) Controllers
Chapter 3120
Enabling and Disabling Input/Output (I/O)
Controllers
DMP allows you to turn off I/O to a host I/O controller so that you can
perform administrative operations. This feature can be used for
maintenance of controllers attached to the host or of disk arrays
supported by VxVM. I/O operations to the host I/O controller can be
turned back on after the maintenance task is completed. You can
accomplish these operations using the vxdmpadm command provided
with VxVM.
In active/active type disk arrays, VxVM uses a balanced path mechanism
to schedule I/O to multipathed disks. As a result, I/O may go through any
available path at any given point in time. For example, if a system has an
active/active storage arrayinterface board that is connected to this disk
array (if supported by the hardware), you can use the vxdmpadm
command to list the host I/O controllers that are connected to the
interface board. Disable the host I/O controllers to stop further I/O to the
disks that are accessed through the interface board. You can then replace
the board without causing disruption to any ongoing I/O to disks in the
disk array.
In active/passive type disk arrays, VxVM schedules I/O to use the
primary path until a failure is encountered. To change an interface card
on the disk array or a card on the host (if supported by the hardware)
that is connected to the disk array, disable I/O operations to the host I/O
controllers. This shifts all I/O over to an active secondary path or to an
active primary path on another I/O controller so that you can change the
hardware.
After the operation is over, you can use vxdmpadm to re-enable the paths
through the controllers.