FC Public Group
This functionality is available in: Storage > FC Targets > Fibre Channel groups > Public group
What is an FC public group
A public group is a group of one or more Fibre Channel ports. Fibre Channel port groups help you organize and manage LUN mappings more easily. FC Public Group gives access to assigned volumes to any initiator that is able to connect to the FC target ports assigned to a given group.
IMPORTANT! It is recommended to use FC Public Group only with peer-to-peer FC connections to avoid unexpected behavior.
A public group is present on a pool by default and cannot be removed or created. Initially, no volumes or targets are assigned to this group, so nothing is available until it is configured manually. Devices available in such a group are visible globally, and there is no need to configure Fibre Channel Initiator by assigning WWN using GUI.
Functionalities within the public group
Within the public group, you can:
- Deactivate group - causes that access to the data in the group is no longer valid.
- Add target - specifies access to a public group for a given target.
- Attach an existing zvol - attaches an existing zvol to a public group.
- Add a new zvol - creates a new zvol. The options available here are described in this article.
In the case of an existing zvol, you can edit, delete, detach it from the group, and add it to a backup task, but for the Fibre Channel targets it is only possible to detach a zvol from a group.
While it might be convenient to use this feature as it removes the necessity to configure initiators that will have access to the group resources, it might cause unwanted side effects for configurations that utilize an FC switch. Note that using an FC public group may lead to the following on the initiator's side:
- An unauthorized system connected to the same public group can gain access to FC resources.
- Unpredicted system states, e.g. creating a multipath.
Note! You cannot add a target to a public group when it is assigned to another Fibre Channel group. The same target cannot be assigned to two groups that share a set of initiators.
What must be taken into considerations/risks
When the FC switch is used, and any of the server FC ports in initiator mode is also connected to that switch, it will cause the server to connect the volumes added to the public group. This behavior is caused by the fact that the public group allows connections from any initiator, including the initiator mode ports of the server that are connected to the same FC switch. In other words, the server will simply connect to itself. As a result, volumes exported by the server will be visible as connected to the server disks - it behaves as some sort of a loopback. Moreover, depending on the number of ports running in initiator mode connected to the same switch as target ports, the same volume might be connected to the server multiple times, creating a multipath configuration if that feature is enabled. The safest way to avoid this situation is to use the public group only for ports that are directly connected without utilizing the switch. In the case of FC switches, those devices usually allow the configuration of zones that describe which switch ports are logically interconnected. Zones may also be used to resolve described issues, but it might simply move the configuration effort from the FC group initiators configuration to the FC switch zone configuration.
More information about Fibre Channel groups can be found here.