HP Veritas Volume Manager 5.0 -UX 11i v3 manual Typical arrangement of a 2-node campus cluster

Creating and administering disk groups

Handling conflicting configuration copies

191

Figure 4-1 Typical arrangement of a 2-node campus cluster

Node 0	Redundant private	Node 1
	network
	Fibre Channel
	switches
	Disk enclosures
enc0		enc1
Building A		Building B

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 -foption 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