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

Enabling and Disabling Input/Output (I/O) Controllers
110 VERITAS Volume Manager Administrator’s Guide
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 array and you need
to change an interface 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.
Displaying DMP Database Information
You can use the vxdmpadm command to list DMP database information and perform
other administrative tasks. This command allows you to list all controllers that are
connected to disks, and other related information that is stored in the DMP database. You
can use this information to locate system hardware, and to help you decide which
controllers need to be enabled or disabled.
The vxdmpadm command also provides useful information such as disk array serial
numbers, which DMP devices (disks) are connected to the disk array, and which paths are
connected to a particular controller.
For more information, see “Administering DMP Using vxdmpadm” on page 112.