Understanding the domains in the optical fiber Storage Network

Understanding how Fiber Channel (FC) recognizes domains and new mechanisms for virtualizing Fiber Channel Networks Helps you further understand and study these concepts. Building a storage LAN (SAN) is not difficult-you only need to put things in it-but it is difficult to make it easy to cope with various changes. In this article, we will learn about the fiber channel domain, address allocation, and virtual storage LAN (VSAN ).

Switch

First, we must first understand a SAN fiber channel network without closed loops. Everything you see here looks similar to the Spanning Tree. Of course, there are some different terms, but the same concepts also apply.

When the Fiber Channel switch goes online, a dynamically assigned Domain_ID (domain ID) is obtained ). Next, the master switch (PS) selects the process to start. This process is very similar to the process of selecting the root bridge of the tree, and then the Domain_ID (domain ID) allocates the process.

Before a vswitch can communicate with other vswitches, it will first set itself to know the connected devices. Skip link initialization. We only need to simply know that the hardware will calculate the current port type and decide the N port address to connect. The FCID (Fiber Channel address) is obtained through the Domain_ID (domain ID), Area_ID (Region ID), and WWN (Global name) of the connected port, and then the switch assigns the FCID to each connected port.

The following briefly describes how the selection process determines the primary switch:

Clear the Domain_ID (domain ID) List;

In the link between vswitches (Port E), transmit Fiber Channel Network Construction (BF) frames. Do not send BF frames to ports that have already sent BF frames to you, to avoid loops;

Wait for the Network Stability of the fiber channel to ensure that BF frames are fully transmitted throughout the network;

Transmit an EFP (Fiber Channel Network Parameter switching) frame and send a SW_ACC (switch accepted) to the transmitter of each EFP frame );

Check the EFP frame and find the PS_Priority (primary switch priority), PS_Name (Global name of the primary switch node), and Domain_ID (domain ID) list;

Connect the primary switch priority with the primary switch name, and select the minimum number;

Repeat this process until all connected devices reach an agreement on the primary switch.

After the master switch selects a process, the switch must start the Domain_ID (domain ID) allocation process. Even if the Domain_ID is set manually, the assignment process is still started because the primary switch needs to compile the Domain_ID list. Domain_ID selection process is not very important, because most people manually set the domain. We only need to know that changing the Domain_ID will cause each device to re-Send the EFP frame according to the updated information.

Setting Domain_ID (domain ID) is very important because if the current Domain_ID conflicts with each other, the process of merging the fiber channel network may be interrupted. If you only have one vswitch and want to expand the fiber channel network and merge the two networks, if both of them are Domain_ID 1 (the default factory settings of the manufacturer), an error will occur. Before connecting to the fiber channel network, each new switch must be set to a unique Domain_ID.

When using a virtual storage LAN (VSAN), Domain_ID conflicts often occur. Except for fiber channel networks, the virtual storage LAN is the same as the virtual LAN. You can set a vswitch (usually Cisco) that supports virtual storage LAN to different ports and different fiber channel networks. The node connected to Port 1 may belong to fiber channel network 322, while another node next to this node may belong to network 4; two completely isolated networks. Each fiber channel network may be a domain 31-this is just an example. In most cases, except for the whimsical scenarios of a few vendors, fiber channel networks do not have routes. Therefore, nodes in different networks cannot communicate with each other. This is good, but in many cases we need to merge the two networks.

Generally, two fiber channel networks can be merged by connecting multiple switches. If a "core" switch is already connected to the other two switches, and suddenly decides to merge the fiber channel network and place them in the same virtual storage LAN, it is recommended that all these switches have a unique Domain_ID. Otherwise, because FCID contains Domain_ID, network transmission will suddenly become very unstable. In addition, the master switch of each domain has its own name server, which contains information about port N. If the received frame contains information in conflict with it, then the switch cannot determine how to send.

Virtual Fiber Channel Network Model

Like a virtual LAN, a virtual storage LAN can set any boundary, which reduces the complexity of management compared to manual cabling. Cisco's virtual storage LAN technology is widely used because ANSI (American National Institute of Standards) is very recognized for its use and called it "virtual Fiber Channel Network ". The virtual storage LAN is more flexible than the Ethernet Virtual LAN.

The virtual Fiber Channel network model advances virtualization to a level. It can set up a regional server so that all nodes connected to the fiber channel network know how to connect to the network. In the IP world, services (such as DHCP and DNS) are generally run by the host, and here the Fiber Channel service is run by the switch. In the virtual storage LAN environment, the switch actually runs the Fiber Channel service once for each fiber channel network.

When talking about the Fiber Channel service, here are some common Fiber Channel addresses related to the storage LAN Service. The brief list is as follows:

0xFF FF F5: Multicast Server

0xFF FF F6: clock synchronization server

0xFF FF F7: KDC (Key Distribution Center)

0xFF FF F8: alias server (for multicast or search groups)

0xFF FF F9: QoS (Service Quality) Information

0xFF ff fa: managing servers

0xFF ff fb: Time Server

0xFF ff fc: Directory Server

0xFF ff fd: Fiber Channel Network Controller

0xFF ff fe: Optical Fiber Channel network login server

FCID is not necessary for SCSI that is above the running of the fiber channel. Because unicast fiber-channel frames are transmitted back and forth between the global names (WWN) of nodes, the fiber-channel address: link Initialization is required only in two cases, or transmit IP addresses over the fiber channel. When an IP address is transmitted over an optical fiber channel, the IP address must be converted to an optical fiber channel address. Similar to the Ethernet world, IP address translation protocol (ARP) is also used in the fiber channel field ). Either the "address interpretation protocol on Fiber Channel" or the fiber channel address interpretation protocol (FARP)-two different protocols-can be applied, and the protocol used depends on which Protocol the device supports. Now you can understand why there are so many interconnection problems in Fiber Channel?

Next we will discuss the network partition and switch settings of the fiber channel.

Summary:

Only when one switch controls the Domain_ID (domain ID) allocation process, the master switch selects the process to start;

A fiber channel domain is a vswitch. Each vswitch runs its own naming service, but the complete list is allocated by the primary switch;

The global name of the node (WWN) is required for sending SCSI over the fiber channel. FCID is still important when other protocols are supported.