Virtual Fabrics

Virtual Fabrics is a procedure to partition a Switch in to Logical switches. Each switch has its own data, control, and management paths.

Virtual Fabrics are called VSAN in CISCO so don’t get confused when someone asks about Virtual Fabrics.

Logical Switches:

Logical switches are the fundamental for Logical Fabrics. When Virtual fabrics are enabled a switch can be divided in to multiple logical switches. Ports and resources of switch can be shared dynamically to the logical switches.

Logical Switch features:

• A Logical Switch can be configured in any mode, including McDATA Fabric or McDATA Open Fabric mode.
• Allocate fabric resources per port rather than per switch
• Simplify chargeback for storage by customer, department, application, or storage tier
• Consolidate resources across multiple fabrics
• Logical fabrics can be deployed Non Disruptively in existing SAN environment.
• Improved ISL bandwidth utilization.

Logical switches are divided in to three.

1. Default Logical Switch.
2. Logical Switch.
3. Base Switch.

1. Default Logical Switch:

             Default Logical switches are created when Virtual fabrics are enabled.

            Default Logical switches contains all the physical ports and resource.

            In a Switches a ports to other logical switches can be assigned through chassis administrator.

     2. Logical Switch:

            User creates logical switches.

            Ports and resource to the logical switches are assigned from Default logical switches through Chassis administrator.

     3. Base Switch:

            Base switch is a user defined switch.

            In a Physical switch only one Base switch can be present.

            Base switch provides a methodology for other logical switches to communicate with each other.

            Connection between two Base switches is called Extended Inter switch links.

            Logical switches are having Fabric ID assigned to every logical switches.

            This FCID helps switches to communicate with each other through XISL.

            When Logical switches with the same FID are configured to use the Base Switches automatically create a Logical ISL within the XISL.

            LISL isolates traffic from multiple fabrics.

            LISL is dedicated to traffic for a single fabric.

Device Login Process

Device Login process is a process when a new devices gets connected to a Fabric it gets registered with fabric so that it can communicate with other devices in the Fabric.

A device communicating in the fabric can be a Host server with Solaris, windows, Linux or a storage device. All kind of devices need to be registered with Switch for communicating with other devices.

Device Login process categorized in to 2 process a. FLOGI b. PLOGI

Below mentioned is the process explaining the Device Login process:

I have tried to categorize Device login in to steps. Now let’s look in to it.

FLOGI:

FLOGI is a process where a Device gets it Fabric address which is a 24 Bit address.

Step 1 (FLOGI)

FLOGI (Fabric Login) the first frame transmitted by an Node device that is attempting to attach to a switch.  The FLOGI contains many bits of information about this initializing end device (N_Port).

Step 2 (FLOGI ACC)

Switch will respond to the FLOGI with an FLOGI ACC.  The format of the FLOGI ACC is identical to the FLOGI request but the information contained within it will be specific to the responding switch/switch port and Fabric Identifier gets assigned to Node.

Step 3 (PLOGI Name Server):

Node port sends a PLOGI signal to Name server so that node is able to register with and send queries to the Name Server.

Step 4 (PLOGI ACC):

Switch will respond the node port request for port Login with Acknowledgement.

Step 5 (Register with the Name Server):

Once PLOGI gets acknowledged then Node port can register with Name server for discovery of Target storage devices or SAN Devices.

Step 6 (Name Server Accepts registrations):

Name server accepts the Node ports registration with Name server.

Step 7 (SCR – State Change Registration):

Node Port will request the switch Fabric controller to send it a Registered State Change Notification (RSCN) every time something in the fabric changes.

Step 8 (State Change Registration ACK):

Fabric controller will accepts the SCR notification request with the switch.

Step 9(Query Name server):

Query Name server for the list of devices Node port can contact with in a fabric.

Step 10(Name server response):

Name server will respond to the Node port request and it will send the list of devices it can contact.

In this Device login process we could see that Fabric services like Fabric Login, Name server and Fabric controller participate in device Login process.

Some services are used in Zoning, In my next post I will explain Zoning and Switch services used in Zoning.

Brocade Fabric OS

Brocade fabric OS helps us to configure, manage and maintain a SAN as per needs of user.

Fabric OS Core Functions

1. Automatic discovery of devices: Fabric devices log in to the Simple Name Server SNS). Translative mode is automatically set to allow fabric initiators to communicate with private loop targets.
2. Universal port support: Fabric OS identifies port types and automatically initializes each connection specific to the attached Fibre Channel system, whether it is another switch, host, private loop, or fabric-aware target system.
3. Continuous monitoring of ports for exception conditions: Fabric OS disables data transfer to ports when they fail.

Brocade supports various Fabric services for reconfiguration of Brocade switches as per fabric needs. Now Let’s Discuss about Brocade fabric services.

In My next post I will be explaining how this fabric services are being used using Device login process

Fabric Login Services:

• The Fabric Login server assigns a fabric address to a fabric node, which allows it to

Communicate with services on the switch or other nodes in the fabric.

• The fabric address is a 24-bit address (0x000000) containing three 3-byte nodes.

Directory Services:

• The directory server or name server registers fabric and public nodes and conducts queries to discover other devices in the fabric.

Fabric Controller: 

• Fabric controller provides State Change Notifications (SCNs) to registered nodes when a change in the fabric topology occurs.

 Time Server: 

• Time server sends the time to the member switches in the fabric from the principal switch.

 Management server: 

• Single point for managing the Fabric or switch.
• Allows a SAN management application to retrieve information and administer interconnected switches, servers, and storage devices.
• The management server assists in the auto discovery of switch-based fabrics and their associated topologies.

Alias server: 

• Helps to assign single name for group of nodes or WWPN.

Broadcast server: 

• When frames are transmitted to address FFFFFF, then frames are replicated to all the nodes N and NL ports. I have never seen this address being used it is a optional fabric services.

 Brocade provides Dynamic Routing Services for high availability and maximum Performance:

1. Dynamic path selection via link-state protocols: Uses Fabric Shortest Path First (FSPF) to select the most efficient route for transferring data in a multi switch environment.

1. Load sharing to maximize throughput through Inter-Switch Links (ISLs): Supports high throughput by using multiple ISLs between switches.
2. Automatic path failover: Automatically reconfigures alternate paths when a link fails. Fabric OS distributes the new configuration fabric wide and reroutes traffic without manual intervention.
3. In-order frame delivery: Guarantees that frames arrive in order.
4. Automatic rerouting of frames: When a fault occurs reroutes traffic to alternative paths in the fabric without interruption of service or loss of data.
5. Support for high-priority protocol: Ensures that frames identified as priority frames receive priority routing to minimize latency.
6. Static routing support: Allows network managers to configure fixed routes for some data traffic and ensure resiliency during a link failure.
7. Automatic reconfiguration: Automatically reroutes data traffic onto new ISLs when they are added to the SAN fabric.

Management of Brocade switches using End to End Management:

1. Management Server based on FC-GS-3.
2. SNMP Agent.
3. In Band using External IP Interface.
4. Syslog Daemon interface.
5. Switch Beaconing.

Brocade optional Services: 

1. Zoning: 

Zoning is a fabric-based service that enables you to partition your storage area network (SAN) into logical groups of devices that can access each other. 

2. Encryption services:

The in-flight encryption and compression features allow frames to be encrypted or compressed at the point of an ISL between two Brocade switches, and then to be decrypted or decompressed at the ingress point of the ISL.

3. Web Tools:

A web tool provides a GUI interface to manage the brocade switches.

4. Quick Loops:

Brocade OS excludes intelligent hubs by creating virtual loops and this virtual loops provides the function of Hub.

5. Extended Fabrics:

 Extended Fabrics re configures the switch to support the rigors of transmitting I/O  over long distances in conjunction with technologies such as Dense Wave Division Multiplexing (DWDM)