Bug 1503061

RHEL LVM documentation describes below steps to migrate a volume group from one system to another:

https://access.redhat.com/documentation/en-US/Red_Hat_Enterprise_Linux/6/html/Logical_Volume_Manager_Administration/VG_move.html

The steps in above link suggests to use "vgexport" to export the volume group after deactivating it with "vgchange -an" command.

Couple of users had a query about what is a significance of using "vgexport" after deactivating the vg with "vgchange -an" command? since deactivation of the volume group would prevent any access to the lvm volumes present in it.

The users had also checked the man page of "vgexport" but were unable to find more information about significance of using "vgexport" after deactivating the volume group.


So, this BZ is filled to add some more information to the man page of "vgexport" to provide some more information about how doing vgexport before a volume group migration could help to avoid accidental access to the vg and benefit of using vgexport.

I have a suggestion to add a summary similar to the one below to man page of "vgexport" to provide more information on benefit of vgexport:


----8<----
Once the volume group is in exported state, any accidental attempt to activate the volume group or lvm volumes present in it would fail with an error.

While migrating the physical volumes, volumes groups from one system to another, once the volume group is de-activated, there is still a risk that any scheduled backup jobs, automation scripts, or applications which are configured to use specific lvm volume/volume group may try to access the volume group when it is in de-activated state. It may also try to activate the volume group.

And if the volume group accidentally gets activated during migration process, then it could lead to lvm, filesystem metadata corruption.

To avoid any chances of above risk, we could export the volume group from system before a migration. It would prevent any further access or changes in the volume group.

For example, an attempt to re-activate the volume group or lvm volumes in exported vg fails with following error:


	[root@testhost ~]# vgchange -an vg1
	  Volume group "vg1" is exported		<---
	[root@testhost ~]# 
	[root@testhost ~]# lvchange -ay vg1/lv1
  	  Volume group vg1 is exported
	[root@testhost ~]# 
	[root@testhost ~]# 

    Accidental removal of PV from VG also fails with similar error:

	[root@testhost ~]# vgreduce vg1 /dev/mapper/mpatha
	  Volume group vg1 is exported
	  Cannot process volume group vg1
	  Failed to find physical volume "/dev/mapper/mpatha".


Once the volume group is exported from system, it would be available on any system only after re-importing it. Thus it would add an additional layer of security for volume group when it is being migrated from one system to other. It would prevent the volume group from activation or any accidental changes.
----8<----

Version-Release number of selected component (if applicable):
lvm2-2.02.130-5.el7.x86_64

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