SLVM Online Volume Reconfiguration (September 2009)

• When lvcreate, lvmerge , lvremove, or lvsplit is used, the logical volume device special files are
automatically added or removed only on the nodes sharing the volume group.
/etc/lvmtab and /etc/lvmtab_p
The /etc/lvmtab file is not changed during online configuration of shared volume groups because
/etc/lvmtab only applies to Version 1.0 volume groups. Online configuration of shared volume
groups only applies to Version 2.1 volume groups.
The /etc/lvmtab_p file is changed on all the nodes sharing a Version 2.1 volume group when the
volume is extended (vgextend) or reduced (vgreduce). Adding or removing an alternate link only
changes the local /etc/lvmtab_p file.
When the shared volume group is extended (a physical volume is added), the /etc/lvmtab_p file
of the node on which the vgextend command is issued (the server node) is augmented with the
physical volume path given on the command line (might be a legacy or a persistent device special file
name). However, on the client nodes, /etc/lvmtab_p is always augmented with the persistent
physical volume device special file name.
When the shared volume group is reduced (a physical volume is removed), all the links to this
physical volume are removed from the /etc/lvmtab_p file of the nodes sharing the volume group.
Activating a shared volume group
If the volume group was extended or reduced or if logical volumes were created or removed from
node B while the volume group was not activated on node A, before activating the volume group on
the node A, you must follow these steps:
1. Issue the following command on node B:
vgexport -s -p -m map_name vg_name
2. Issue the following command on node A:
vgexport vg_name
3. Copy the map_name map file from node B on node A as follows:
vgimport [-N] -m map_name -s vg_name
4. Activate the volume group shared on node A.
You must use vgexport and vgimport to update the /etc/lvmtab_p file and the volume group
directory (to add or remove logical volumes device special files) on node A. The /etc/lvmtab_p
file and the volume group directory are updated automatically only on the nodes sharing the volume
group. If the volume group is deactivated on a node, it is not sharing it.
Alternate PV links
An alternate PV link is a local entity. It has a meaning only in the context of one node because the
paths to a device can differ from one node to the other. As a result, when an alternate path is added
to a volume group (vgextend), the effect is local only. The path is added in the local
/etc/lvmtab_p file and nothing is added in the remote /etc/lvmtab_p file.
While the volume group is activated shared, you can add alternate links (vgextend) on the server
only.