what is the difference between "vgcfgbackup & vgcfgrestore" and "vgexport & vgimport"

vgcfgbackup : creates a backup of the LVM configuration extent within the volume group.

vgcfgbackup -f /tmp/vg01 vg01
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vgcfgrestore : Use this to restore the LVM configuraztion on a physical disk, for instance, after it has been replaced. When the LV on a replaced disk is not mirrored, a vgcfgrestore is rather useless, but when your LV is mirrored, you can resync your mirror to the new disk after a vgcfgrestore.

The following procedure will require a valid prior LVM volume group configuration file and also a map file.

1. Make sure the volume group is deactivated.

# vgchange -a n /dev/<vgname>
Volume group "<vgname>" has been successfully changed.
2. Verify the PV list in the configuration file shows the previous configuration. In this case we are assumming that the user added a second disk to the VG, old configuration file will show only one:

# vgcfgrestore -f /dev/lvmconf/<vgname>.conf.old
Volume Group Configuration information in "<vgname>.conf.old"
VG Name /dev/<vgname>
 ---- Physical volumes : 1 ----
    /dev/rdsk/c#t#d0 (Non-bootable)
3. Restore the VG header information from previous configuration file. It should be restore to the old physical volume.

# vgcfgrestore -f /etc/lvmconf/<vgname>.conf.old /dev/rdsk/c#t#d#
Volume Group configuration has been restored to /dev/rdsk/c3t15d0
4. Remove VG configuration out of the lvmtab.

# vgexport /dev/<vgname>
5. Recreate VG directory:

# mkdir /dev/<vgname>
6. Recreate the volume group "group" node file. Remember that the minor number must be unique.

# mknod /dev/<vgname>/group c 64 0x0#0000
7. Reimport the volume group. LV structures will be recover from map file.

# vgimport -m /tmp/<vgname>.map /dev/<vgname> /dev/dsk/c#t#d#
Warning: A backup of this volume group may not exist on this machine.
Please remember to take a backup using the vgcfgbackup command after activating the volume group.
8. Reactivate volume group. Some warning messages may be received.

# vgchange -a y /dev/<vgname>
Volume group "<vgname>" has been successfully changed.
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vgexport : Gathers the physical disks and LV-number/name mapping to configuration files and removes the VG configuration from the LVM, but leaves all information on disk intact.
vgexport -vps -m vg_pas_dvebmgs.map /dev/vg_pas_dvebmgs
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vgimport : Reads the above configuration files to add a VG to the LVM setup, but the data on the disks itself should already be there.
vgimport -vs -N -m vg_pas_dvebmgs.map /dev/vg_pas_dvebmgs
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vgcfgrestore/vgcfgbackup : Backups the LVM configuration on disk for pure restore/recovery reasons.
vgexport/vgimport : Backups LVM layout to allow you to move the disks to another system and import the configuration there.