About server-based I/O fencing

In a disk-based I/O fencing implementation, the vxfen driver handles various SCSI-3 PR based arbitration operations completely within the driver. I/O fencing also provides a framework referred to as customized fencing wherein arbitration operations are implemented in custom scripts. The vxfen driver invokes the custom scripts.

The CP server-based coordination point uses a customized fencing framework. Note that SCSI-3 PR based fencing arbitration can also be enabled using customized fencing framework. This allows the user to specify a combination of SCSI-3 LUNs and CP servers as coordination points using customized fencing. Customized fencing can be enabled by specifying vxfen_mode=customized and vxfen_mechanism=cps in the /etc/vxfenmode file.

Figure: Customized fencing displays a schematic of the customized fencing options.

Figure: Customized fencing

Customized fencing

A user level daemon vxfend interacts with the vxfen driver, which in turn interacts with GAB to get the node membership update. Upon receiving membership updates, vxfend invokes various scripts to race for the coordination point and fence off data disks. The vxfend daemon manages various fencing agents. The customized fencing scripts are located in the /opt/VRTSvcs/vxfen/bin/customized/cps directory.

The scripts that are involved include the following: