Input/Output Fencing

What Does Input/Output Fencing Mean?

Input/output (I/O) fencing is a method of preventing data corruption in a clustered and shared-storage computer environment by isolating a malfunctioning node.


A cluster contains a group of computers linked together so that they are all aware of each other’s existence and current status. They can access the same data via the effective sharing of storage. Clustered servers provide high availability and, to a limited extent, load balancing across database access. I/O fencing is a mechanism where if any node starts malfunctioning in the computer cluster environment, then that node gets isolated automatically so it cannot access shared data via I/O operations.

Techopedia Explains Input/Output Fencing

It is important to have a proper mechanism to identify the malfunctioning node by other active nodes. Otherwise, there may be a chance that the malfunctioning node understands that it is the healthy one and the other nodes are malfunctioning. This could create a race condition, where all nodes try to access shared resources, such as a shared database, possibly leading to a corrupted database.

Conceptually, I/O fencing is simple enough, but its execution varies between clustering and database software vendors. Often, complex databases use this technology, which is most often found on fibre-channel storage area network (SAN) arrays.

Vendor specific examples of I/O fencing are as follows:

  • Oracle Parallel Server (OPS) at a database level.
  • Red Hat Global File Server (GFS) at a file system level.
  • Veritas Cluster Server (VCS) at a platform and database-agnostic level.

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Margaret is an award-winning technical writer and teacher known for her ability to explain complex technical subjects to a non-technical business audience. Over the past twenty years, her IT definitions have been published by Que in an encyclopedia of technology terms and cited in articles by the New York Times, Time Magazine, USA Today, ZDNet, PC Magazine, and Discovery Magazine. She joined Techopedia in 2011. Margaret's idea of a fun day is helping IT and business professionals learn to speak each other’s highly specialized languages.