VERITAS Volume Manager 3.5 Migration Guide (September 2004)

Chapter 2

Converting LVM to VxVM

Converting LVM Volume Groups to VxVM Disk Groups

This section outlines the process for converting LVM volume groups to VxVM disk groups.

NOTE It is recommended that you read through this section carefully before 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 only raw disks, recreate the conﬁguration in VxVM, and then 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 application access to user data in the

volume groups undergoing conversion. Access to the LVM conﬁguration itself (the metadata of LVM) must

also be limited to the conversion process.

Volume Group Conversion Limitations

There are certain LVM 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 the conversion of LVM to VxVM, the areas of the disks used 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.

NOTE You can use the vxcp_lvmroot (1M) command to create a VxVM root disk on a spare

physical disk from the contents of the existing LVM root disk. Similarly, you can use the

vxres_lvmroot (1M) command to recreate an LVM root disk on a spare disk from the

contents of the VxVM root disk. For more information, see the section “Rootability” in the

“Administering Disks” chapter of the VERITAS Volume Manager Administrator’s Guide.

• A volume group containing mirrors using the Mirror Write Cache feature for volume consistency recovery.