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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Note It isrecommendedthat you readthroughthissection carefullybefore beginning any
volume group conversion.
The conversion process involves many steps. Though there are tools to help you with the
conversion, some of these steps cannot be automated. You should be sure to understand
how the whole conversion process works, and what you will need to do in the process
before beginning a volume group conversion.
The tool used for conversion is vxvmconvert. This interactive, menu-driven program
walks you through many of the steps of the process of converting volume groups for use
by VxVM. Using vxvmconvert can reduce the downtime associated with converting
from LVM to VxVM. Without the vxvmconvert tool, the only possible method of
conversion would be to take full backups of user data, destroy the existing LVM
configuration leaving onlyraw disks, recreatethe configurationin VxVM, andthen reload
the user data.
The vxvmconvert process converts LVM volume groups to VxVM disk groups in place.
In reality, the utility changes disks within LVM volume groups to VxVM disks by taking
over the areas of the disks used for LVM configuration information, and creating the
equivalent VxVM volume configuration information. User data, the portions of the disks
used for file systems, databases, etc., are not affected by the conversion.
The act of conversion changes the names by which your system refers to the logical
storage. For this reason, the conversion process is necessarily an off-line one. There can be
no applicationaccess to user data inthe volume groups undergoing conversion. Access to
the LVM configurationitself (themetadata ofLVM) must also be limitedto theconversion
process.
Volume Group Conversion Limitations
There are certainLVM volume configurations that cannot be converted to VxVM.Some of
the reasons a conversion could fail are:
◆ A volume group with insufficient space for metadata.
In theconversion ofLVM to VxVM,the areas ofthe disksused to store LVM metadata
are overwritten with VxVM metadata. If the VxVM metadata that needs to be written
will not fit the space occupied by the LVM metadata, the group containing the disk
cannot be converted. If you have just enough space for the conversion, you probably
would want to have more space for future configuration changes.
◆ A volume group containing the root volume.
vxvmconvert does not convert any volume group that contains a rootable volume,
identified by the presence of the LIF area as created by mkboot(1M). Not only is the
current root volume off limits, but any volume that might be used as an alternate root
volume is rejected as well.