LVM2-4

It is possible to configure LVM2 to operate with LVM1-formatted (Red Hat Enterprise Linux 3) volume groups. You can even configure LVM2 to default to using the LVM1 metadata format. This can be done by editing the /etc/lvm/lvm.conf file and ensuring that the following directive is enabled in the global section:
format = "lvm1"
The change made above is global and permanent. If you are attempting to recover or import an LVM1 volume, use the -M1 switch to force the LVM2 tools to use the LVM1 metadata format. For example if you have a LVM1-formatted volume group you want to restore:
vgcfgrestore -M1
Now that the volume group is restored, change the metadata of the newly restored volume group to LVM2 to retain compatibility with the Red Hat Enterprise Linux 4 LVM tools.
vgconvert -M2
See the respective man pages of these commands for more information and additional options: man vgcfgrestore and man vgconvert.