Red Hat Knowledgebase

This exact behavior can be seen if the volume group was created before the logical volume manager (lvm2) is put into clustering mode. This can happen if vgcreate is done before the lvm configuration file (/etc/lvm/lvm.conf) is changed to set locking_type = 2. This change to the lvm configuration file is done when the lvm2-cluster package is installed. If the volume group was created before that package was installed, the clustering flag for the volume group will not be set, and that will cause changes to the underlying logical volumes (in this case, lvresize) to not be propagated throughout the cluster.

If the volume group is linear (i.e. not striped or mirrored), all nodes in the cluster can still access the data successfully. That's because of the way the cluster suite is designed to work independently:

1. GFS can act as a stand-alone filesystem in a non-clustered environment.
2. Cluster suite can manage resources without GFS
3. Volume groups can be used in either clustered or non-clustered environments. However, this also implies that the system may not notice a problem until an operation like lvresize is executed.

The solution is to check the clustering flag for the volume group and turn it on if necessary.

To check if the clustering flag is on for a volume group, use the vgs command and see if the "Attr" column shows a "c".

If the cluster flag is off, the output of vgs looks like this:

[root@localhost ~]# vgs
  VG        #PV #LV #SN Attr   VSize  VFree
  VolGroup00   1   3   0 wz--n- 12.34G 344.00M

If the cluster flag is on, the output of vgs looks like this:

[root@localhost ~]# vgs
  VG        #PV #LV #SN Attr   VSize  VFree
  VolGroup00   1   3   0 wz--nc 12.34G 344.00M

To set the clustering flag on, use this command:

vgchange -cy [volume group name]

Note: Red Hat Enterprise Linux 5 has a new locking_type = 3 in /etc/lvm/lvm.conf.

The logical volume manager can take a new locking_type = 3 to figure out the appropriate locking for clustered and non-clustered volumes.