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
This method is a full LVM restoration which is used to restore your user data from backup when the configuration has changed. This method is used if the VxVM configuration has changes since the conversion. This method restores the LVM configuration information, then restores user data from backup. See “Full LVM Restoration” for more information on using this method.




	NOTE: 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.vgrestore(1M) should not be confused with the LVM command, vgcfgrestore(1M). vgcfgrestore is used to restore the LVM configuration information saved by vgcfgbackup(1M), 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.

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.




	NOTE: In many cases, if you choose the rollback method and the configuration has changed, you receive an error and must use the full restore method. If you used the workaround of creating symbolic links from the old LVM names to the new VxVM names described in "step “5. Planning for new VxVM logical volume names” you must remove the symbolic links you created before beginning the rollback. This "snapshot" is kept on the root file system. The presence of this snapshot should not be taken as assurance that full off-line backups will not be needed. See “4. Backing up your LVM configuration and user data” for specific information on backups.

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




	CAUTION: Do not use this option unless you are certain that you want to restore LVM volume groups. Once this is run, the VxVM disks that were created as a result of the original conversion from LVM to VxVM no longer exists. This option is not a full complement to `vxvmconvert`. It simply writes the saved LVM metadata back on top of the disks. Those data can only be considered valid for the period of time when the logical volumes are off-line. If the VxVM configuration has been brought online, the metadata in the rollback snapshot should be considered obsolete. See “Full LVM Restoration” for specific information.

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.




	NOTE: The snapshot of LVM internal data is kept on the root file system.

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:

Use vgrestore to restore LVM internal data.
# vgrestore vol_grp_name
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

Restoring the LVM Volume Group Configuration

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Rollback to LVM Using vxvmconvert

Full LVM Restoration