Veritas Volume Manager 4.1 Administrator's Guide (HP-UX 11i v3, February 2007)

Chapter 4, Creating and Administering Disk Groups
Handling Conflicting Configuration Copies in a Disk Group
151
Typical Arrangement of a 2-node Campus Cluster
A serial split brain condition typically arises in a cluster when a private (non-shared) disk
group is imported on Node 0 with Node 1 configured as the failover node.
If the network connections between the nodes are severed, both nodes think that the other
node has died. (This is the usual cause of the split brain condition in clusters). If a disk
group is spread across both enclosure enc0 and enc1, each portion loses connectivity to
the other portion of the disk group. Node 0 continues to update to the disks in the portion
of the disk group that it can access. Node 1, operating as the failover node, imports the
other portion of the disk group (with the -f option set), and starts updating the disks that
it can see.
When the network links are restored, attempting to reattach the missing disks to the disk
group on Node 0, or to re-import the entire disk group on either node, fails. This serial
split brain condition arises because VxVM increments the serial ID in the disk media
record of each imported disk in all the disk group configuration databases on those disks,
and also in the private region of each imported disk. The value that is stored in the
configuration database represents the serial ID that the disk group expects a disk to have.
The serial ID that is stored in a disk’s private region is considered to be its actual value.
If some disks went missing from the disk group (due to physical disconnection or power
failure) and those disks were imported by another host, the serial IDs for the disks in their
copies of the configuration database, and also in each disk’s private region, are updated
Node 0
Fibre Channel
Switches
Disk Enclosures
enc0 enc1
Node 1
Building A Building B
Redundant
Private Network