Veritas Volume Manager 5.0 Administrator's Guide (September 2006)

130 Administering dynamic multipathing (DMP)
Enabling and disabling I/O for controllers and storage processors
Enabling and disabling I/O for controllers and storage
processors
DMP allows you to turn off I/O for a controller or the array port of a storage processor so
that you can perform administrative operations. This feature can be used for maintenance
of HBA controllers on the host, or array ports that are attached to disk arrays supported by
VxVM. I/O operations to the controller or array port 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 controllers that are connected
to the interface board. Disable the 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 the interface card for an array port or an HBA controller
card on the host (if supported by the hardware) that is connected to the disk array, disable
I/O operations to the array port or to the HBA controller. This shifts all I/O over to an
active secondary path or to an active primary path on another 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.
See “Disabling I/O for paths, controllers or array ports” on page 146.
See “Enabling I/O for paths, controllers or array ports” on page 146.
See “Upgrading disk controller firmware” on page 147.
Note: From release 5.0 of VxVM, these operations are supported for controllers that are
used to access disk arrays on which cluster-shareable disk groups are configured.
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.