Application viewpoint: There are some tips for selecting fiber channel switches

As one of the most important devices in the storage system, fiber channel switches are widely used. I believe many consumers do not know how to buy them, the following is a detailed analysis of the selection of fiber channel switches. The fiber channel network built through the fiber channel (FC) switch is called Fabric or the fiber channel network architecture.

Similar to Ethernet switches, FC switches are usually tightly integrated into the system when most users build storage. On the one hand, users are not very concerned about it, on the other hand, all large storage equipment manufacturers are OEM optical fiber channel switches, and users who are not careful are not even clear about the switch manufacturers.

Basics

In 1980s, the standard method for connecting hosts and storage devices was a point-to-point DAS (direct connection storage) method implemented through interfaces such as IDE or parallel SCSI. Parallel SCSI provides relatively fast access to the SCSI hard disk (5 MBps or 10 MBps), and several hard disks can be connected to the computer through the same interface.

However, as the storage subsystem grows larger, computers become faster and faster, and a new problem arises: external storage devices become larger. Tape libraries, RAID (cheap redundant disk arrays), and other SCSI devices need more and more space, which requires parallel SCSI connections to be extended from the host. At the same time, the I/O (input/output) rate is also growing, so how to in a large bundle of lines (32 or 64-Bit Data Bus) maintaining signal consistency has become a physical problem. The simple parallel SCSI improved version is designed to increase the data transmission distance and solve the signal consistency problem. However, they are ultimately difficult to overcome the technical challenge of high-speed signal transmission under the parallel SCSI bus architecture.

To meet these new requirements, a fiber Channel protocol is developed to provide Gigabit serial network access for storage devices. On the Layer 4 of the fibre channel protocol, a SCSI protocol for Storage Based on the fiber channel is established, an IP protocol for the network, and a virtual interface (VI) for the cluster mapped to the network architecture.) protocol. The Optical Fiber Channel Protocol combines many advantages, such as a network range of up to 10 kilometers, you can use simple serial cables with multiple media, Gigabit network speeds, and multiple protocols on the same cable. These features enable fiber channel protocol as a replacement for parallel SCSI protocol to be recognized throughout 1990s. Currently, fiber channel protocol is used on the vast majority of high-capacity, high-end direct connection storage devices.

As the Fiber Channel Protocol emerged as a point-to-point alternative to parallel SCSI, and gradually became accepted by the market, the emergence of a new technology that combines pure Storage applications and Network technologies-Storage Area Network (SAN ). A san is a network composed of storage devices and system components. All communications are completed on a fiber channel network and can be used to centralize and share storage resources. SAN not only provides high-performance connections to data devices, but also improves data backup speed and redundant connections to the storage system, providing support for high-availability cluster systems.

Simply put, SAN is a dedicated fiber-channel network that connects storage devices and servers. It has a similar architecture with Ethernet, ethernet is composed of servers, Ethernet NICs, Ethernet hubs/switches, and workstations. SAN is composed of servers, fiber channel cards, fiber channel hubs/switches, and fiber channel storage devices, SAN frees large-capacity and long-distance connections from SCSI, and avoids Ethernet limitations to enable high-speed data transmission.

SAN consists of three basic components: interfaces (such as SCSI, fiber channel, ESCON, etc.), connection devices (switching devices, gateways, routers, hubs, etc) and Communication Control Protocols (such as IP and SCSI ). These three components, coupled with additional storage devices and servers, constitute a SAN system. The key device that makes up the network in the storage area is the optical fiber switch (Fiber Channel Switch. Based on the fiber channel topology, A Fiber Channel switch is used to connect the storage system to the server to provide high-speed data transmission and data sharing, and merge local data backup and storage. Fiber Channel networks play an important role in the storage system. It can discover everything in the storage system and manage and control everything in the storage system (1 ).

Technology

Fiber Channel switches provide Fiber Channel switching for high-bandwidth and Low-latency data communication. Currently, fiber channel switches provide connectionless services (Class2 and 3 ). An optical fiber switch is directly connected using an optical fiber network route. It uses routing software to directly connect the initiator and target, so that all the bandwidth of the optical fiber can be exclusive. This means that each connection in the optical fiber can exist independently and does not interfere with other connections. The number of ports of an optical fiber switch ranges from 8 to 64, or even more, including SMART switching hardware, so that any two points of all ports of the switch can be connected. Fiber switches can be stacked through E_Ports. This method can extend the fiber network to thousands of nodes, and the number of switch stacks can reach up to 239.

A large SAN is implemented by connecting multiple switches in a mesh network. Each vswitch has a one-way connection to other vswitches in the network. In the example in Figure 2, The vswitch used has port 16. As the number of switches in the network increases, the percentage of ports used for inter-Switch Connection increases. This is one of the reasons why the FC switch port is expensive. In a mesh SAN core network consisting of six switches with a total of 96 ports, there are 30 vswitches and 66 user ports.

Vswitches greatly improve the performance of optical fiber networks, such as name services, management services, and more complete device connection protocols. Vswitches are used in most environments as a complete mechanism to provide host-to-array connections, especially in multi-device and multi-boot environments. Fiber Channel switches are at the core of SAN storage architecture. The fiber channel switch is logically the core of SAN and connects hosts and storage devices. Fabric infrastructure can be seen as the foundation of SAN. When a device sends a frame of data to the switch, the switch routes the frame to the target device. In fact, a frame can be forwarded before it is fully received. Fiber Channel switches are also intelligent. They can provide various Fabric services, including services for locating other nodes on the Network (simple name service). They can automatically establish routes with other switches in Fabric, you can also partition devices to monitor and handle errors.

Fiber Channel switches provide many different functions, including GBIC, Fan redundancy and power supply, partitioning, ring operation, and multi-management interfaces. Each function increases the operability of the entire switching network. Understanding these features can help users design a powerful large-scale SAN. The main functions of an optical fiber switch are as follows: Self-configured ports, loop device support, switch cascade, adaptive speed detection, configurable frame buffering, and partitioning (based on physical ports and WWN-based partitions) IP over Fiber Channel (IPFC) broadcast, remote logon, Web management, Simple Network Management Protocol (SNMP), and SCSI interface independent device Service (SES. Optical fiber switches are often divided into different categories based on their functions and features. Generally, the hardware may be based on the same basic architecture or the same ASIC chip, but the software functions are different. The price of the Fiber Channel switch is determined based on the requirements it can meet. A high-redundancy core-level switch is an exception. It is often developed and designed based on its own hardware fault-tolerant platform. The following describes the different features of vswitches of various major categories.

Entry-level switch

Entry-level switches are mainly used in small working groups with 8 to 16 ports. They are suitable for low-price scenarios with little need for expansion and management. They are often used instead of hubs to provide higher bandwidth and more reliable connections than hubs. Generally, entry-level switches are not purchased separately, but are often purchased together with other vswitches to form a complete storage solution. Entry-level switches provide limited port cascade capabilities. Users may encounter some manageability problems when using such low-end devices separately.

Workgroup-level optical fiber switch

Fiber switches provide the ability to cascade many switches into a large-scale Fabric. By connecting one or more ports of two vswitches, all ports connected to the vswitch can see a unique network image, any node on this Fabric can communicate with other nodes. Essentially, through cascade switches, a large, virtual, and distributed switch can be created, and the distance between them can be very large. Fabric built on multiple vswitches looks like a Fabric composed of independent vswitches, the ports on all vswitches can view and access all other ports on Fabric just like accessing a local vswitch. The unified name server and management service allow you to view and modify all Fabric information through a separate interface.

An important factor in creating a distributed Fabric is to obtain the bandwidth for connections between switches. The effective rate between any two ports is affected by the valid bandwidth of the switch connection. You may need to use connections between multiple switches to maintain the necessary bandwidth. The Working Group has a large number of fiber channel switches and is more common. You can use workgroup switches in multiple ways, but the most widely used field is small-sized SAN. This type of switch can be connected by the interconnection lines between the switches to provide more ports. The interconnection lines between switches can be created on any port on the fiber channel switch. However, if you plan to use products from multiple vendors, you must ensure that the devices are interoperable.

Core-level optical fiber switch

A core-level switch (also called a guide) is generally located in the center of a large SAN, connecting several edge switches to form a SAN network with hundreds of ports. The core switch can also be used as a separate switch or edge switch, but its enhanced functions and internal structure make it work better in the core storage environment. Other features of core switches include: support for protocols other than optical fiber (like InfiniBand), support for 2 Gbps Optical fiber channels, and advanced optical fiber services (such as security, trunk lines, and frame Filtering ).

Core-level optical fiber switches generally provide many ports, from 64 ports to 128 ports. It uses a very wide internal connection to route data frames with the maximum bandwidth. These switches are used to establish a network with a wider coverage and provide greater bandwidth. They are designed to route frame signals with the shortest latency between multiple ports as quickly as possible. In addition, core optical fiber switches often adopt "Blade-based hot swappable circuit boards": as long as the switch board is inserted into the cabinet, new functions can be added, or online repair can be performed, it can also achieve phased on-demand online scaling. Many core-level switches do not support arbitration rings or other directly connected loop devices. They only focus on core switching capabilities.

Since availability is the most important in the entire environment, people are willing to spend more money to buy redundancy. All components of a High-redundancy switch are redundant, removing single points of failure completely, it also ensures a very long running time. The cost of redundancy is generally spent on High Availability backboards, power supplies, redundant circuits, and software that maintains availability. This type of switch has many built-in logic circuits used to handle hardware faults in the switch. In addition to redundancy, core-level optical fiber switches support non-disruptive service software upgrades, eliminating the need for system maintenance during the upgrade. The alternate path is a type of redundancy level on the network. It can be configured with an elastic dual Fabric, which completely eliminates single point of failure, it can avoid serious network consequences caused by software or hardware errors, fire, natural disasters, or operation errors. For most high-availability networks, you should select a dual-channel network built by the core optical fiber switch. Core switches provide the highest reliability and port density. In data centers with a large number of fiber channel infrastructure, such products are almost pervasive and centralized storage switches.

Purchase

Whether a small number of switches are used to build a simple storage network, or a large number of switches are used to form a large and scalable core storage network, You must select the brand and model of each fiber channel switch. As vswitches are the core component of building a storage area network SAN, it is crucial to select the most suitable vswitch. Only the correct selection of the most suitable fiber channel switch for the Storage Area Network can improve the efficiency of enterprise information management and meet the most challenging requirements. Compared with other technical implementations, the selection of fiber channel switches is a strategic decision. You must understand the current IT situation and requirements of enterprises, at the same time, it is necessary for the selected switch to meet the future development needs of enterprises. Factors affecting final decision-making include scalability, compatibility, and interoperability with other hardware devices. It is worth noting that the network in any storage area is not static, and it is always faced with problems of expansion and integration with new technologies and new products. The storage Region network meets future needs through flexible scalability, thus protecting users' investment.

Scalability includes two aspects: one is how to expand to a larger Fabric when the original system cannot meet the storage requirements of users with the expansion of the storage network; the other is, with the development of technology, we can smoothly upgrade to new technologies and applications. For example, the development of IP Storage makes it important for more and more users to consider iSCSI and FCIP. Specifically, you must understand several key points of switch selection. Including hardware redundancy that reflects reliability and availability, the number of ports that reflect the capacity of network nodes, and the network functions required to meet the needs of a specific application environment, and the budget of the Network Project for the storage area. The first step in selecting a vswitch is to determine the number of servers and storage devices to connect. When selecting a vswitch, there are several general principles for reference: For networks with fewer than eight devices and with no expansion plan, an eight-port switch is enough, if you plan to expand to more than 8 devices in the future, you need to consider a 16-port switch. If there are more than 16 devices in the network, you should consider using multiple 16-port switches for Cascade.

If you want to ensure uninterrupted operation of key services, you need to build a system in redundancy mode. You can consider the dual-Optical Fiber switching network configuration scheme. Because this network topology ensures redundancy, you can use cheaper single-power switching devices. Even if an fibre Channel Switch fails, the link switching software on the host and storage array automatically switches the communication to redundant devices until the faulty device is replaced. If regular downtime maintenance does not affect enterprise applications, it is cost-effective to use a switch with hot swappable power supply and fan, it also ensures that any single point of failure of the power supply or fan does not affect the network operation.

In short, there are a lot of considerations before you choose which Fiber Channel switch to use to establish a SAN optical switching network, just like other equipment procurement plans, before comparing fiber channel switches, we need to clarify the current and future key requirements, as well as the priority levels of these requirements.