<span>About setting up I/O fencing</span>


About setting up I/O fencing
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About setting up I/O fencing

Figure: Workflow to configure I/O fencing illustrates the tasks involved to configure I/O fencing.

Figure: Workflow to configure I/O fencing

I/O fencing requires the coordinator disks be configured in a disk group. The coordinator disks must be accessible to each node in the cluster. These disks enable the vxfen driver to resolve potential split-brain conditions and prevent data corruption.

Review the following requirements for coordinator disks:

You must have three coordinator disks.

The coordinator disks can be DMP devices or iSCSI devices.

You must use DMP disk policy for iSCSI-based coordinator disks.

For the latest information on supported hardware visit the following URL:

http://entsupport.symantec.com/docs/283161
Each of the coordinator disks must use a physically separate disk or LUN.

Symantec recommends using the smallest possible LUNs for coordinator disks.
Each of the coordinator disks should exist on a different disk array, if possible.
The coordinator disks must support SCSI-3 persistent reservations.
Symantec recommends using hardware-based mirroring for coordinator disks.
Coordinator disks must not be used to store data or must not be included in disk groups that store user data.
Coordinator disks cannot be the special devices that array vendors use. For example, you cannot use EMC gatekeeper devices as coordinator disks.

The I/O fencing configuration files include:

/etc/vxfendg

You must create this file to include the coordinator disk group information.

/etc/vxfenmode

You must set the I/O fencing mode to SCSI-3.

You must configure the vxfen module to use DMP devices or iSCSI devices, and set the SCSI-3 disk policy as dmp.

/etc/vxfentab

When you run the vxfen startup file to start I/O fencing, the script creates this /etc/vxfentab file on each node with a list of all paths to each coordinator disk. The startup script uses the contents of the /etc/vxfendg and /etc/vxfenmode files.

Thus any time a system is rebooted, the fencing driver reinitializes the vxfentab file with the current list of all paths to the coordinator disks.

Note:

The /etc/vxfentab file is a generated file; do not modify this file.

An example of the /etc/vxfentab file on one node resembles as follows:

/dev/vx/rdmp/c1t1d0
/dev/vx/rdmp/c2t1d0
/dev/vx/rdmp/c3t1d0

In some cases you must remove disks from or add disks to an existing coordinator disk group.

Warning:

If you remove disks from an existing coordinator disk group, then be sure to remove the registration and reservation keys from these disks before you add the disks to another disk group.

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