Chapter 8. Configuring Fencing using SCSI Persistent Reservations

A registration occurs when a node registers a unique key with a device. A device can have many registrations. For our purposes, each node will create a registration on each device.

A reservation dictates how a device can be accessed. In contrast to registrations, there can be only one reservation on a device at any time. The node that holds the reservation is know as the "reservation holder". The reservation defines how other nodes may access the device. For example, Red Hat Cluster Suite uses a "Write Exclusive, Registrants Only" reservation. This type of reservation indicates that only nodes that have registered with that device may write to the device.

Red Hat Cluster Suite is able to perform fencing via SCSI persistent reservations by simply removing a node's registration key from all devices. When a node failure occurs, the fence_scsi agent will remove the failed node's key from all devices, thus preventing it from being able to write to those devices.