Disk Access Across the SAN Fabric

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 Disk Access / Storage access process occurs when the server is powered on which is connected to SAN fabric. The main components involved at the higher level are Server, SAN Switches, and Storage Array.  Successful completion of the above process will create a link between Server and Storage, which helps in disk access.


The steps involved in as follows

FLOGI - Fabric LOGIn process :

When the server Host Bus Adapter(HBA) power on, it will send its WWNN and WWPN. Using the details shared by the server HBA the switch will assign FCID(Fibre Channel ID) to each HBA and is stored in an internal database. This FCID is used in routing the host request to its storage. This FCID is equivalent to an IP address in the host. 


FC NAme Service:

Once the FCID is allocated by the initial switch connected to Server in the fabric, will now share this information with all other switches in the same fabric. The database within the switch which stores the FCID to WWN mapping is called the FCNS database. With this now all other switches in the same fabric know where to route the read/write request from Storage/Server.

the switch command "show fcns database" can be used to display the information stored in the FCNS database.



PLOGI  :

PLOGI is the process of initializing the device port on the switch and port registration in the Name Server. The switch port facing the end node is called "F port" and the end device port is called "N port".The port connected between the switch is called the "E port". With this, the switch now determines whether the end device is a switch/server/storage and port speed. Before this a proper zoning has to be created between the server and storage,


PRLI - PRocess LogIn:

Process  Login is the Process of establishing communication between the two "N port" i.e., during this process the server sends a PRLI request to Storage. If zoning and masking are configured properly then a communication link is created between the storage and server.


This completes the brief description of the server login process to the fabric. See you all in the next blog.........:-)



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