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Creating and administering volume sets 365

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-onlyread-write}] \[-oindex] [-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 -ocompvol_access=read-writeoption is specified, direct writes are allowed to the raw device of each component volume. If the value is set to 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