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. Usingvxvmconvert 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.

  Note    The most likely scenario in which a Volume Group cannot be converted, because of insufficient private space, is when a large HP-UX system using "Extent based Striping" is being used
• 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 thevxres_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.

Users should be aware that when converting mirrored LVM volumes to VxVM, some of these volumes will likely have the Mirror Write Cache consistency recovery method in force on the volume. The vxvmconvert utility can convert these volumes, but must use the Dirty Region Logging (DRL) feature to obtain the same level of functionality. However, since Dirty Region Logging requires some user space to be available for the log, a conversion could fail due to an MWC volume being full, leaving no space for the DRL log. However it is very unlikely that this situation would occur. Note that the MWC and DRL are used only when the system crashes or is improperly shut down, to quickly bring all mirrors in the volume back into a consistent state.

• A volume group containing the /usr file system.

For this release, a volume group containing the /usr file system cannot be converted because vxvmconvert needs access to files in /usr.

• Volume groups with any dump or primary swap volumes.

vxvmconvert will not convert any volume group with dump or primary swap volumes. These are volumes known to the boot process. However, swap volumes on volumes other than the root volume can be converted (as long as this volume is not in the same volume group as the root volume).

• Volume group disks used in MC/ServiceGuard clusters.

The conversion process does not support conversion of any volume group that is marked as a member of a MC/ServiceGuard or OPS Edition high availability cluster. The volume group must be deactivated and removed from membership in the high availability cluster before it can be converted.

• Volume groups used for cluster lock disks.

The conversion process does not support conversion of a volume group that contains a disk that is being used for a cluster lock disk for an MC/ServiceGuard cluster.

• Volume groups with any disks that have bad blocks in the bad block directory.

Unlike LVM, VxVM does not support bad block revectoring at the physical volume level. If there appear to be any valid bad blocks in the bad block directory of any disk used in an LVM volumegroup, the group cannot be converted. See Appendix A, Conversion Error Messages, for actions to take in this situation.

• Volume groups with mirrored volumes.

A conversion fails if the LVM volume group being converted has mirrored volumes, but the system does not have a valid license installed that enables mirroring for VxVM.

The analyze option in vxvmconvert, which is described in later sections, aids you in identifying which volume groups can be converted.