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

About I/O fencing
I/O fencing protects the data on shared disks when nodes in a cluster detect a
change in the cluster membership that indicates a split-brain condition.
The fencing operation determines the following:
■ The nodes that must retain access to the shared storage
■ The nodes that must be ejected from the cluster
This decision prevents possible data corruption. The installer installs the I/O
fencing driver, VRTSvxfen, when you install Storage Foundation Cluster File
System HA. To protect data on shared disks, you must configure I/O fencing after
you install and configure Storage Foundation Cluster File System HA.
I/O fencing technology uses coordination points for arbitration in the event of a
network partition.
See “About preventing data corruption with I/O fencing” on page 31.
Note: Symantec recommends that you use I/O fencing to protect your cluster
against split-brain situations.
About I/O fencing for Storage Foundation Cluster File System HA in
virtual machines that do not support SCSI-3 PR
In a traditional I/O fencing implementation, where the coordination points are
coordination point servers (CP servers) or coordinator disks, Veritas Clustered
Volume Manager and Veritas I/O fencing modules provide SCSI-3 persistent
reservation (SCSI-3 PR) based protection on the data disks. This SCSI-3 PR
protection ensures that the I/O operations from the losing node cannot reach a
disk that the surviving sub-cluster has already taken over.
In virtualized environments that do not support SCSI-3 PR, Storage Foundation
Cluster File System HA attempts to provide reasonable safety for the data disks.
Storage Foundation Cluster File System HA requires you to configure non-SCSI3
server-based I/O fencing in such environments. Non-SCSI3 fencing uses CP servers
as coordination points with some additional configuration changes to support I/O
fencing in such environments.
About preventing data corruption with I/O fencing
I/O fencing is a feature that prevents data corruption in the event of a
communication breakdown in a cluster.
31Storage Foundation Cluster File System architecture
About I/O fencing