What is I/O fencing and how does it work?
I/O fencing is used in cluster environments to make sure that two or more nodes do not access a file system simultaneously. I/O fencing is important to prevent corruption on shared storage in a cluster. It is called I/O fencing because we can compare it to putting a fence between the node that wants to access the storage device and the storage device itself. There are two common methods to prevent this access.STONITH (shoot the other node in the head) is a technique that automatically powers down a node that is not working correctly to prevent access to a shared resource. This may seem like a rough method to shut down computers, but it is better to shut down a cluster node than to spend hours recovering a corrupted file system because multiple nodes were trying to access it simultaneously. The other method, called data-based fencing, works by maintaining a list of nodes that should be allowed to access a shared device. If a node is not on the list, it will not be allowed to access the device. I/O fencing is needed in any situation where high availability is offered and where multiple hosts could potentially write to the same file system simultaneously.
This was first published in May 2013