In Fibre Channel
protocol, a registered state change notification
) is a Fibre Channel fabric
's notification sent to all specified nodes
in case of any major fabric changes. This allows nodes to immediately gain knowledge about the fabric and react accordingly.
Implementation of this function is obligatory for each Fibre Channel switch
, but is optional for a node. This function belongs to a second level of the protocol, or FC2
Some events that trigger notifications are:
- Nodes joining or leaving the fabric (most common usage)
- Switches joining or leaving the fabric
- Changing the switch name
The nodes wishing to be notified in such way need to register themselves first at the Fabric Controller, which is a standarized FC virtual address present at each switch.
RSCN and zoning
If a fabric has some zones
configured for additional security, notifications do not cross zone boundaries if not needed. Simply, there is no need to notify a node about a change that it cannot see anyway (because it happened in a separate zone).
For example, let's assume there is a fabric with just one node, namely a server's FC-compatible HBA
. First it registers itself for notifications. Then a human administrator connects other node, like a disk array
, to the fabric. This event is known at first only
to a single switch, the one that detected one of its ports going online. The switch, however, has a list of registered nodes (currently containing only the HBA node) and notifies every one of them. As HBA receives the notification, it choses to query nearest switch about current list of nodes. It detects a new disk array and starts to communicate with it on a SCSI
level, asking for a list of SCSI LUNs
. Then it notifies a server's operating system
, that there is a new SCSI target containing some LUNs. The operating system auto-configures those as new block devices
, ready for use.