Raw device node access to component volumes

Article:HOWTO59595  |  Created: 2011-10-12  |  Updated: 2011-10-12  |  Article URL http://www.symantec.com/docs/HOWTO59595
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Raw device node access to component volumes

To guard against accidental file system and data corruption, the device nodes of the component volumes are configured by default not to have raw and block entries in the /dev/vx/rdsk/diskgroup and /dev/vx/dsk/diskgroup directories. As a result, applications are prevented from directly reading from or writing to the component volumes of a volume set.

If some applications, such as the raw volume backup and restore feature of the Symantec NetBackup™ software, need to read from or write to the component volumes by accessing raw device nodes in the /dev/vx/rdsk/diskgroup directory, this is supported by specifying additional command-line options to the vxvset command. Access to the block device nodes of the component volumes of a volume set is unsupported.

Warning:

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 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.

See Enabling raw device access when creating a volume set

See Displaying the raw device access settings for a volume set

See Controlling raw device access for an existing volume set

See About volume sets


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Article URL http://www.symantec.com/docs/HOWTO59595


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