Restoring the LVM Volume Group Configuration

In some circumstances, you may need to restore the LVM configuration that existed before you converted to VxVM with vxvmconvert. For example:

• If something went wrong during the conversion, such as a system crash or a disk crash that caused the conversion to be unworkable.
• If during a conversion only some of a set of volume groups converted successfully, then you may want to restore the LVM configuration for the entire set.

It is possible to restore the original LVM configuration in one of two ways, but both have limitations and restrictions. The method you use depends on if any changes have been made to the VxVM configuration since the conversion occurred. Any of the following actions changes the VxVM configuration:

• adding or removing disks
• adding or removing volume groups
• changing the names of VxVM objects

Restoration methods include:

• rollback using vxvmconvert

Use rollback only if the VxVM configuration has not changed since the conversion. This method restores the LVM configuration without the need for user data restoration. See Rollback to LVM Using vxvmconvert for details on using this method.

• restore user data using vgrestore and frecover

This method is a full LVM restoration which is used to restore your user data from backup when the VxVM configuration has changed since the conversion was made. First of all, this method restores the original LVM configuration information (vgrestore), and then restores the original user data from the backup that was made before the conversion was done (frecover). See Full LVM Restoration for more information on using this method.

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  Note    Restoring user data using the vgrestore and frecover method will result in the loss of all user data changes made since the conversion, and the loss of all new volumes created since the conversion.

In other words, this method of restoring data will take you back to exactly where you were before the conversion was done.

However, if no new volumes have been created, and if none of the existing volumes have been resized, you can use the vxvmconvert rollback option to restore the original LVM configuration. If you use this method, any user data changes made since the conversion will be retained, and you will not need to carry out a user level data restore (frecover).

The name changes that vxvmconvert makes as part of the conversion are managed by rollback, and do not count as VxVM configuration changes for the purposes of choosing a restoration method.

The vgrestore command should not be confused with the LVM command, vgcfgrestore. vgcfgrestore is used to restore the LVM configuration information saved by vgcfgbackup, but it will not restore your device files and/etc/fstab entries. It also will not import and activate the volume group, nor will it clean up any VxVM information left around. However, vgrestore will do all of this for you.

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Rollback to LVM Using vxvmconvert

Rollback replaces the VxVM disk groups with the original LVM volume groups. During conversion, vxvmconvert saves a "snapshot" of the original LVM metadata and associated configuration files, such as /etc/fstab and LVM device files. It restores only the LVM metadata and configuration files from this snapshot; user data is not changed. This method can only be used if no changes have been made to the configuration since the conversion.

For example, if a disk has been added to the disk group or if the names of any logical volumes have changed, you cannot use the rollback method.

To rollback to LVM from the VxVM conversion, run vxvmconvert and choose option 3. See Example: VxVM to LVM rollback for illustration.

Full LVM Restoration

If you need to restore the original LVM configuration, but changes have been made to the VxVM configuration, you cannot use the rollback option of vxvmconvert. In this case, you must restore the user data in addition to restoring the old LVM metadata and associated configuration files. You may need to use this method if the disks in use by the LVM/VxVM volumes were corrupted during or after conversion.

To use this method, you must have backed up data located on all the volume groups' logical volumes before conversion to VxVM.

Restoration of LVM volume groups is a two-step process consisting of a restoration of LVM internal data (metadata and configuration files), and restoration of user or application data.

The process is limited to restoring the state of the logical volumes as they existed prior to conversion to VxVM disks. If the data has changed on the volumes during the time they were VxVM volumes, those changes are lost once you restore the LVM configuration and saved user data.

To do a full restoration of the original LVM configuration, do the following:

1. Use vgrestore to restore LVM internal data.
     # vgrestore vol_grp_name
2. Use the recovery method to restore user or application data. In preparation for conversion, the recovery method should have been done with the standard backups you made in preparation for conversion. The following example shows an frecover from the fbackup example in "step 4. Backing up your LVM configuration and user data."
     # mount -F vxfs /dev/vg01/lvol3 /foodir
     # frecover -r -f /dev/rmt/c0t0d0BEST