The fencing mechanism of SCX has been enhanced to make it optional. Though it is recommended to use strong fencing mechanisms, some user environments require flexibility and in such cases, fencing can be turned off.
Basics
* The fencing can be set a) globally or b) Individual disks.
* Fencing type cannot be changed for disks configured as Quorum devices.
* Fencing type set at individual disk level will take precedence over global settings.
By default, the cluster will use Device ID (DID) pathcount to determine the type of reservation protocol to be used. For devices connected to 2 nodes, it will be PGR emulation and for 3 or greater connections, SCSI will be used.
How to determine what is the fencing type globally?
bash-3.00# scdidadm -G
The cluster is currently configured to use DID path count algorithm to determine fencing protocol for shared devices.
Now let us change the fencing type globally to nofencing:
bash-3.00# scdidadm -G nofencing
Warning: Device instance d1 is a quorum device - fencing protocol remains PATHCOUNT for the device.
Now to change the fencing algorithm to prefer scsi,
bash-3.00# scdidadm -G prefer3
** If scsi cannot be used for a subset of disks, the warning message will be displayed.
To return fencing to default settings,
bash-3.00# scdidadm -G pathcount
To change fencing at per disk level, use scdidadm with -F option:
To change the fencing type to noscrub,
bash-3.00# scdidadm -F nofencing-noscrub d2
** noscrub switches fencing off without scrubbing the scsi keys. Keys are scrubbed only for scsi and not for PGRe.
For using global fencing settings,
bash-3.00# scdidadm -F useglobal d2