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

357Creating and administering volume sets
Raw device node access to component volumes
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 120 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 is 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.
The following example creates a volume set, myvset1, containing the volume, myvol1,
in the disk group, mydg, with raw device access enabled in read-write mode:
# vxvset -g mydg -o makedev=on -o compvol_access=read-write \
make myvset1 myvol1
Displaying the raw device access settings for a volume set
You can use the vxprint -m command to display the current settings for a volume set. If
the
makedev attribute is set to on, one of the following is displayed in the output: