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

Discovering and Configuring Newly Added Disk Devices
70 VERITAS Volume Manager Administrator’s Guide
Adding Foreign Devices
DDL may not be able to discover some devices that are controlled by third-party drivers,
such as those that provide multipathing or RAM disk capabilities. For these devices it may
be preferable to use the multipathing capability that is provided by the third-party drivers
for some arrays rather than using the Dynamic Multipathing (DMP) feature. Such foreign
devices can be made available as simple disks to VxVM by using the vxddladm
addforeign command. This also has the effect of bypassing DMP for handling I/O. The
following example shows how to add entries for block and character devices in the
specified directories:
# vxddladm addforeign blockdir=/dev/foo/dsk chardir=/dev/foo/rdsk
By default, this command suppresses any entries for matching devices in the
OS-maintained device tree that are found by the autodiscovery mechanism. You can
override this behavior by using the -f and -n options as described on the vxddladm(1M)
manual page.
After adding entries for the foreign devices, use either the vxdisk scandisks or the
vxdctl enable command to discover the devices as simple disks. These disks then
behave in the same way as autoconfigured disks.
The foreign device mechanism was introduced in VxVM 4.0 to support non-standard
devices such as RAM disks, some solid state disks, and pseudo-devices such as EMC
PowerPath. This mechanism has a number of limitations:
◆ A foreign device is always considered as simple disk with a single path. Unlike an
autodiscovered disk, it does not have a DMP node.
◆ It is not supported for shared disk groups in a clustered environment. Only
standalone host systems are supported.
◆ It is not supported for Persistent Group Reservation (PGR) operations.
◆ It is not under the control of DMP, so enabling of a failed disk cannot be automatic,
and DMP administrative commands are not applicable.
◆ Enclosure information is not available to VxVM. This can reduce the availability of
any disk groups that are created using such devices.
If a suitable ASL is available for an array, these limitations are removed, as described in
“Third-Party Driver Coexistence” on page 65.