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Although the specs indicate that Fabric Notifications can be sent by Fibre Channel switches or end-devices, today they are only sent by Fibre Channel switches (and directors) to end-devices. When the Fibre Channel switch detects a link integrity or congestion event, it will notify registered end-devices. The central role of the Fibre Channel switches in the SAN allows them the best visibility to other switches and end-devices.
End-devices such as storage portsmust first register for Fabric Notifications. Only end-devices registered for Fabric Notifications will be notified of events. By being selective about what end-devices Fabric Notifications are sent to, unnecessary traffic is minimized.
Please note that it is not necessary for all components of the SAN to register for Fabric Notifications in order for the customer to see huge benefits. For example, a storage array can register for Fabric Notifications and receive link integrity and congestion events (from the switch) that are caused by older HBAs (that do not support Fabric Notifications). In cases where an older HBA (which doesn’t support Fabric Notifications) causes fabric issues, such issues will be detected by the switch and reported to the storage array.
With congestion, Congestion Signal Primitives can be used instead of FPIN ELS messages if the underlying hardware supports it and negotiates for it. The use of these signals is advantageous since congestion ELS messages can get queued behind congested traffic resulting in delays in delivering these notifications to end-devices. By using signals instead of ELS messages, congestion notifications effectively “cut the line” and flow through to the end-devices unabated.
Below are the four event types defined by the spec:
Please note that not all the information contained in the Fabric Notification messages is displayed by the Dell management tools. At a minimum, the following is displayed: