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365Creating and administering volume sets
Raw device node access to component volumes
Caution: Writing directly to or reading from the raw device node of a component
volume of a volume set should only be performed if it is known that the volume's
data will not otherwise change during the period of access.
All of the raw device nodes for the component volumes of a volume set can be
created or removed in a single operation. Raw device nodes for any volumes
added to a volume set are created automatically as required, and inherit the
access mode of the existing device nodes.
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