VERITAS Volume Manager 4.1 Administrator's Guide

Administering Dynamic Multipathing (DMP)
Enabling and Disabling Input/Output (I/O) Controllers
Chapter 3128
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.
NOTE These operations are not supported for controllers that are used to access disk
arrays on which cluster-shareable disk groups are configured.