SLVM Online Volume Reconfiguration (September 2009)

On node2:
# lvcreate -M y -m 1 -l 10 vg_bigmir
lvcreate: The logical volume "/dev/vg_bigmir/lvol1" could not be created
as a special file in the file-system:
File exists
In /var/adm/syslog/syslog.log:
LVM: VG 128 0x005000: the distributed configuration failed 13 0 0 204.
LVM: node node4.corp.com 3 failed with 17
SNOR
Using the vgchange –x option, SLVM SNOR enables you to change the configuration of a shared
volume group, and of logical and physical volumes in that volume group, while keeping it active in a
single node. Using this procedure, applications on at least one node are available during the volume
group reconfiguration.
Prior to SLVM SNOR, suppose you had an HP Serviceguard cluster set up on three nodes with data
shared in the cluster using common storage. You use SLVM to create and manage volume groups
shared across all nodes of the cluster. Applications access the volume group for data read and write
operations from disk. To change a shared volume group configuration, like creating or modifying
logical volumes and physical volumes, or modifying the volume group (VG) attributes, you must do the
following:
1. Shut down the applications using the VG.
2. Deactivate the VG on all nodes.
3. Activate the VG in exclusive mode on one of the nodes.
4. Change the configuration on the VG.
5. Deactivate the VG.
6. If required, generate the map file with the changed configuration, copy it over, and re-import it to
all the other nodes of the cluster.
7. Activate the VG in shared mode on all the cluster nodes.
8. Restart the applications using the VG.
With the SNOR functionality installed, to change the volume group configuration, follow these steps:
1. Scale the applications using the volume group down to one node. These applications are still
running on that one node.
2. Deactivate the VG on all but one node of the cluster.
3. Change the activation mode of the VG to exclusive in a single node.
4. Change the configuration on the VG.
5. If required, generate the map file with the changed configuration, copy it over, and re-import it to
all the other nodes of the cluster.
6. Activate the VG in shared mode on the single node and then on all the other cluster nodes.
Application and availability considerations
On the cluster node where the volume group stays active, user I/Os are uninterrupted during and
after the activation mode changes from shared to exclusive and back to shared.
On the other cluster nodes where the volume group is deactivated, you must scale the application
down to a single cluster node, causing a loss of redundancy and possibly performance degradation
for that period.