Veritas Volume Manager 5.1 SP1 Administrator"s Guide (5900-1506, April 2011)

Access to the raw device nodes for the component volumes can be configured to
be read-only or read-write. This mode is shared by all the raw device nodes for
the component volumes of a volume set. The read-only access mode implies that
any writes to the raw device will fail, however writes using the ioctl interface or
by VxFS to update metadata are not prevented. The read-write access mode allows
direct writes via the raw device. The access mode to the raw device nodes of a
volume set can be changed as required.
The presence of raw device nodes and their access mode is persistent across system
reboots.
Note the following limitations of this feature:
■ The disk group version must be 140 or greater.
■ Access to the raw device nodes of the component volumes of a volume set is
only supported for private disk groups; it is not supported for shared disk
groups in a cluster.
Enabling raw device access when creating a volume set
To enable raw device access when creating a volume set, use the following form
of the vxvset make command:
# vxvset [-g diskgroup] -o makedev=on \
[-o compvol_access={read-only|read-write}] \
[-o index] [-c "ch_addopt"] make vset
vol [index]
The -o makedev=on option enables the creation of raw device nodes for the
component volumes at the same time that the volume set is created. The default
setting is off.
If the -o compvol_access=read-write option is specified, direct writes are allowed
to the raw device of each component volume. If the value is set to read-only, only
reads are allowed from the raw device of each component volume.
If the -o makedev=on option is specified, but -o compvol_access is not specified,
the default access mode is read-only.
If the vxvset addvol command is subsequently used to add a volume to a volume
set, a new raw device node is created in /dev/vx/rdsk/diskgroup if the value of
the makedev attribute is currently set to on. The access mode is determined by the
current setting of the compvol_access attribute.
Creating and administering volume sets
Raw device node access to component volumes
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