Veritas Storage Foundation 5.1 SP1 Cluster File System Administrator"s Guide (5900-1738, April 2011)

Changes take effect immediately and are lost on the next reboot. For changes to
span reboots you must also update the /etc/llttab file.
Note: LLT clients will not know how things are going until you only have one LLT
link left and GAB declares jeopardy
Split-brain and jeopardy handling
A split-brain occurs when the cluster membership view differs among the cluster
nodes, increasing the chance of data corruption. With I/O fencing, the potential
for data corruption is eliminated. I/O fencing requires disks that support SCSI-3
PGR.
Jeopardy state
In the absence of I/O fencing, SFCFS installation requires two heartbeat links.
When a node is down to a single heartbeat connection, SFCFS can no longer
discriminate between loss of a system and loss of the final network connection.
This state is defined as jeopardy.
SFCFS detects jeopardy and responds to it in ways that prevent data corruption
in some split-brain situations. However, data corruption can still occur in other
situations:
■ All links go down simultaneously.
■ A node hangs and is unable to respond to heartbeat messages.
To eliminate the chance of data corruption in these scenarios, I/O fencing is
required. With I/O fencing, the jeopardy state does not require special handling
by the SFCFS stack.
Jeopardy handling
For installations that do not support SCSI-3 PGR, jeopardy handling prevents
some potential split-brain conditions. If any cluster node fails following a jeopardy
state notification, all cluster file systems that were mounted on the failed node
or nodes are disabled on all remaining nodes. If a leave reconfiguration happens
after jeopardy state notification, then the nodes which have received the jeopardy
state notification leave the cluster.
Storage Foundation Cluster File System architecture
Split-brain and jeopardy handling
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