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The Device Discovery Layer (DDL) may not be able to discover some devices that are not auto-discoverable, such as RAM disks. Such foreign devices can be made available as simple disks to Veritas Volume Manager (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.
Foreign device support has the following limitations:
A foreign device is always considered as a 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.
The I/O fencing and Cluster File System features are not supported for foreign devices.