VERITAS Volume Manager 3.5 Migration Guide (August 2002)

Chapter 2, Converting LVM to VxVM
Final 24 July 2002 Converting LVM Volume Groups to VxVM Disk Groups
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Non-file system back up
If a logical volume you are converting does not contain a file system, and is being used
directly by an application (such as a database application), use the backup facilities
provided by the application. If no such facility exists, consider using the dd command.
5. Planning for new VxVM logical volume names
When you change from LVM volumes to VxVM volumes, the device names by which
your system accesses data are changed. LVM creates device nodes for its logical volumes
in /dev under directories named for the volume group. VxVM creates its device nodes in
/dev/vx/dsk and /dev/vx/rdsk. When conversion is complete, the old LVM device
nodes are gone from the system, and the system will access data on the device nodes in
/dev/vx.
This change in names can present problems. Any application that refers to specific device
node names will be at risk when these names change. Similarly, any files that record
specific device node names for use by applications can be problematic.
The most obvious area where this problem arises is in /etc/fstab. To handle this
problem, vxvmconvert will rewrite the fstab with the new VxVM names when
conversion isdone so that fsck, mount,and related utilitieswill behave as theydid prior
to the conversion.
There are potentially many other applications, though, that may be put at risk by the
name changes in conversion. vxvmconvert cannot help with these. The system
administrator must examine the mechanisms used in each of the following areas to see if
they reference LVM device names:
◆ Databases run on raw logical devices may record the name of that device node.
◆ Backup systems may do device level backups based on device node names recorded
in private files. Also labeling of the backups may record device names.
◆ Scripts run by cron(1M).
◆ Other administrative scripts.
A Workaround
vxvmconvert records a mapping between the names of the LVM device nodes and
VxVM device nodes. This data can be used to create symbolic links from the old LVM
volume to the new VxVM device names. The mapping is recorded in the file:
/etc/vx/reconfig.d/vgrecords/vol_grp_name/vol_grp_name.trans
This file provides information on how to proceed further to link the old LVM volume
names to the new VxVM device names.