Fibre Channel HBAs, hubs, and switches

Posted on November 01, 2000

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SPECIAL REPORT

An excerpt from the 2000 Storage Area Network Report provides market and technology details on key Fibre Channel components.

By Tom Coughlin, Farid Neema, and Dennis Waid

Whether you're expanding your storage area network (SAN) or just planning one, it is critical to understand the core components used in storage networks.

These include host bus adapters (HBAs), bridges and routers, hubs (unmanaged and managed), and switches (fabric switches, "switching hubs," and directors).

Host bus adapters

The entry to the Fibre Channel fabric is an HBA. It connects a server system bus with an external device. HBAs are made for various bus types and physical connections to the transport mechanism. The most common are HBAs with PCI bus interfaces and short-wave fiber-optic transceivers. HBAs come with software drivers for operating systems, upper-layer protocol support, and support for private loop, public loop, and fabric topologies.

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Most currently installed HBAs have private-loop attachment and SCSI-3 upper-layer protocol drivers. Fabric-capable HBAs are now shipping to meet the demand for switched SANs. The majority of HBAs have a single transceiver for connection to the SAN. However, there are some dual-ported and quad-ported HBAs on the market. Multi-ported HBAs save bus slots by aggregating nodes, but may sacrifice reliability by introducing a single point of failure.

An HBA contains all of the Fibre Channel layers (see Table 1). The FC-0 layer enables the HBA to physically transmit and receive on the link. If fiber optics is used, this connector is a GigaBit Interface Converter (GBIC), Gigabaud Link Module (GLM), or 1X9 transceiver with standard dual SC coupling. In the case of a copper interface, the connector is a DB-9 with four active wires or the HSSDC form factor. The HBA also contains clock and data recovery (CDR) circuitry, serializing/deserializing functions, and a memory buffer and retiming circuit that enables the receipt and transmission of gigabit serial data.

The FC-1 transmission protocol uses on-board 8b/10b encoding/decoding logic for outgoing and incoming data, respectively. This layer also contains low-level link management, flow control, and error-monitoring functions. If the HBA can interface to a loop, the FC-1 layer must be followed by a Loop Port State Machine (LPSM) circuit. This function is typically included with other features on such products as Agilent Technologies' Tachyon controller chip or Emulex's Firefly chips. The HBA provides the protocol for frame segmentation/reassembly, class of service, and credit algorithms. It also provides link services for fabric and port login needed by FC-2. The FC-4 layer usually provides SCSI-3 and IP software drivers for NT, Unix, or Macintosh operating systems.

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The newer HBAs incorporate most functions into an ASIC-based multifunction architecture to reduce price and real estate requirements (see Figure 1). To provide an upgrade path, HBAs typically include flash memory where microcode can be updated. HBAs in the past were used in private arbitrated-loop environments, and earlier compatibility conflicts between attached devices have been mostly resolved. However, with public loops and switched fabrics, there are additional requirements for flash memory to deal with the much larger potential problem of incompatible devices. As a consequence, HBA vendors are engineering generic, stand-ardized products that can support private loop, public loop, and point-to-point fabric on a single adapter.

More sophisticated functions are being added to HBAs to increase their value to end users. Some offer add-on functions such as HBA-based RAID, where the task of striping data across multiple drives from the server CPU is performed on the HBA. Virtual Interface (VI) protocols allow applications ready access to the Fibre Channel transport without passing through CPU-intensive protocol stacks. Advanced diagnostic features, such as SCSI Enclo-sure Services (SES) enable the HBA to be part of the SAN management system.


Figure 1: Host bus adapters incorporate most functions into an ASIC-based multifunction architecture.
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Fibre Channel HBA vendors include Adaptec, Agilent Technologies, Antares Microsystems, Atto Technology, Cambex, ConnectCom, Delphi Engineering, Emulex, Genroco, ICP vortex, Interphase, JNI,

LSI Logic, QLogic, Systran, and VMIC. Currently, Emulex and QLogic are the market-share leaders.

Bridges and routers

Bridging is a one-to-one conversion that takes place between SCSI or ESCON and Fibre Channel. Routing converts between multiple SCSI buses and one or more Fibre Channel ports. Routers monitor the data being sent, and determine where a data packet should go (e.g., read, write, or copy command) by reading a leader on each packet of data. Because the router can read a packet without interfering with a backup, routers (or a routing function) can play an important role in SAN management.


Figure 2: Hubs attach multiple nodes, or devices, to a Fibre Channel Arbitrated Loop (FC-AL), with all nodes sharing the 100MBps bandwidth. In this example, the devices are connected to the hub using Gigabaud Link Modules (GLMs).
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Bridges and routers can be in standalone boxes or integrated within a storage subsystem on "blades." Bridges and routers help extend the life of existing storage infrastructures, enabling a progressive migration to Fibre Channel. As storage networks move toward LAN and WAN interconnectivity, routers may play an important role in a SAN network.

Atto, Chaparral Network Storage, Computer Network Technology (CNT), Crossroads, McData, Pathlight, Storage-Tek, TD Systems, and Vicom are some of the vendors that provide SAN bridges and routers. Crossroads is the market-share leader in terms of units shipped.


Figure 3: Users can migrate from a single hub to a switched fabric with connectivity extending to a wide area network.
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The expansion of SANs and the connection of SAN islands will require SAN interconnects over Ethernet and ATM. In this case, the router connects multiple Fibre Channel nodes to one or more Ethernet or ATM nodes. This may result in routing products using Dense Wave Division Multiplexing (DWDM). Brocade and Inrange have partnered with leading DWDM companies Optical Networks and Sorrento, respectively, to provide such future routing products. Salomon Smith Barney analysts believe storage routing could become a large portion of overall storage networking revenues, including SAN-to-SAN, SAN-to-LAN, SAN-to-MAN, and SAN-to-WAN connectivity.

Hubs

In a SAN configuration, a server gains access to the storage network via a connection to one or more Fibre Channel hubs or switches. These network interconnect devices act in a storage network much as they do in a traditional network.


Table 2: The price per port for hubs is about one quarter of the price per port of a fabric switch.
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A hub attaches multiple nodes to a Fibre Channel arbitrated loop, with all nodes sharing the 100MBps bandwidth (see Figure 2). Note that in Figure 2 the Fibre Channel devices are connected to the hub using Gigabaud Link Modules (GLMs). Other transceivers that are used for these connections are GigaBit Inter-face Converters (GBICs) and 1X9 transceivers. GBICs offer greater flexibility in SAN design by enabling the SAN to mix various media and interface types and to make changes to the topology with less disruption to the system. 1X9s are fixed-function optical transceivers that are permanently mounted on the host system card.

Managed hubs provide limited fault isolation, which is otherwise unavailable in a FC-AL topology, due to their ability to automatically bypass a failed port by controlling port traffic. Hubs typically allow the connection of 7 to 12 nodes, although they can be cascaded for greater connectivity.

The major limitation of hubs is that their bandwidth is shared, and the failure of a single element can disrupt a critical application. Also, only one communication between two nodes can take place.

Hubs are helpful in small configurations. The price per port for hubs is about one quarter of the price per port of a fabric switch (see Table 2).


Figure 4: Current high-growth markets include bridges, routers, switches, and directors. Future growth opportunities are in routers, fabric switches, directors, and SAN appliances.
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Managed hubs can act as an initiator. For instance, a hub can tell a storage subsystem when it's time to back up, or what to back up. Thus, managed hubs enable server-less and LAN-less backup, which is one of the killer applications for SANs. Managed hubs also offer techniques for providing limited statistical information about port status and activity.

Information and notification of failures can be achieved out of band to a separate management station. This interface often uses Simple Network Management Protocol (SNMP) Management Infor-mation Bases (MIBs) as a standard protocol for providing this information.

Vixel and Gadzoox Networks are two of the major hub vendors. To maintain profit margins, as prices for hubs go down, these vendors have been working to migrate into the switch market.

In addition to Gadzoox and Vixel, Fibre Channel hub vendors include Atto, Cambex, Emulex, High Velocity Systems, ICP vortex, StorageTek, and Systran.

Switches

A Fibre Channel switch routes data directly between any two nodes. It has the ability to shift circuit connections as required to support data transmission requests. This type of connection can be expanded to include more than one switch and multiple nodes. In this category of switch, any port on any switch can provide (subject to bandwidth availability) full-speed access to any other port on the network. The network consists of a fabric of linked switches.

A loop switch is basically a logical FC-AL run on a physical fabric switch. It provides true concurrency of transactions and fault isolation. Switches allow simultaneous conversations across their ports at full bandwidth, essentially multiplying bandwidth by the number of connected nodes. Switches, alone or in combination with hubs, can be used to build Fibre Channel fabrics, or switched fabrics of Fibre Channel connections, providing the maximum in connectivity and bandwidth.

It is possible to migrate from a single hub to a switched fabric, with connectivity extending to a wide area network (see Figure 3).


Figure 5: The revenue growth rate for most Fibre Channel components will begin tapering off this year.
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Hub and switch performance is measured by a number of parameters, the most obvious of which are the number of ports and the price. Complexity increases exponentially with the number of ports, but so does the usefulness in a large enterprise environment. Cascading several switches to obtain the same result does have the potential drawback of congested links between switches; careful topology planning is key to avoiding this situation. This has parallels to the LAN-based network as well, but reasonable consideration of topology enables users to readily scale a Fibre Channel fabric with high performance. But there are many other issues and parameters that are equally important, such as the classes of service supported, frame latency, on-line discovery, zoning or partitioning, multicasting (fanning the traffic to multiple outgoing ports simultaneously), and the different availability, serviceability, maintainability, and manageability features.

In an effort to compromise between functionality and price, some vendors have introduced "switching hubs," which enable remote switching or routing of the port. Switching hubs provide the ease of plug-and-play operation with existing SAN servers, storage subsystems, and hubs, without the need for the operating system, firmware, or hardware changes that may be required by fabric switches. These switching hubs are generally somewhat static in their configurations, and require either a scripted or manual management change to support functions like shared tape libraries. Prices are generally halfway between hub and switch prices.

Brocade is the leader in the Fibre Chan-nel fabric switch market. Ancor, the number two player was acquired by QLogic and is expected to become increasingly competitive. Other routing, hub, and director companies are also believed to be advancing on this market segment.

FC-AL storage switch

Where fabric switches use a protocol often referred to as "fabric," a new generation of switches using the arbitrated-loop protocol was recently introduced-the FC-AL storage switch. An FC-AL storage switch can deliver the same concurrency and zoning services offered by a fabric switch.

For those installations using arbitrated loop, FC-AL storage switches eliminate the cost and complexity of a mixed-protocol environment by maintaining the same technology and characteristics of the existing installed base of storage hubs, storage subsystems, and servers. This approach challenges the common misconception that the FC-AL protocol is limited for use only in a shared-bandwidth "loop" topology or that the Fabric protocol is required for a switched topology. FC-AL switches are priced halfway between hubs and fabric switches.

However, an FC-AL-only device is not capable of World-Wide-Name-based zoning because it has no corresponding Simple Name Server registry. As a consequence, because the physical address (AL_PA) assignment in an arbitrated loop is subject to change and can be managed only with software enforcement, the zoning implementation of an FC-AL topology is more limited than that of a fabric switch.

Directors

Directors are high-end storage switches. The most common criteria for directors are:

  • High port density (32 ports or more)
  • Scalability
  • Fully redundant components

The two types of storage directors are ESCON/FICON and Fibre Cha-nnel. ESCON/FICON directors are used in mainframe environments. Mainframes communicate through ESCON (Enterprise System CONnec-tion). FICON (S/390 Fibre CONnectivity) is a more advanced form of connectivity.

ESCON has a transfer rate of 17MBps, a maximum distance of 3 kilometers, and half-duplex throughput. In contrast, FICON has a transfer rate of 100MBps, a maximum distance of 20 kilometers, and full-duplex throughput.

All of these products are extremely reliable, with multiple hardware redundancies. McData and Inrange are the two leaders in the ESCON director market.

Fibre Channel directors are open- systems storage products. McData and Inrange created this market class when they began shipping Fibre Channel director products in 1999 and 2000, respectively. QLogic OEMs Inrange's 64-port Fibre Channel director. Brocade plans to release a 64-port software-based director within the next month, based on the company's 2Gbps ASIC chips. Brocade may release higher port density directors in 2001. All of these director products offer total failover capability through hardware redundancy and, in some cases, software redundancies.

Fibre Channel switch vendors (all categories) include Brocade, Computer Network Technology, Gadzoox, Inrange, McData, StorageTek, QLogic, Systran, and Vixel. Brocade is the market share leader.

Figure 4 shows a view of the SAN network components market based on technology, cost, and growth opportunity. Generally, the growth opportunities are with the higher technology/cost products. Current high-growth markets include bridges, routers, switches, and directors. Future growth opportunities are in routers, fabric switches, directors, and SAN appliances. Figure 5 shows revenue projections for several SAN component groups.

Farid Neema is president of Peripheral Concepts Inc. (www.periconcepts.com).
Tom Coughlin is vice president of storage products and Dennis Waid is president at Peripheral Research Corp. (www.silcom.com/~prc). Both consulting/research firms are in Santa Barbara, CA.


Storage Area Networks-SAN 2000


Infrastructure, Products, and Market Opportunities

Contents

EXECUTIVE SUMMARY

1. OVERVIEW AND MARKET POSITIONING

  • Market Driving Forces
  • Internet and Service providers
  • Storage Networking
  • Positioning SAN and NAS

2. ARCHITECTURE AND TECHNOLOGY

2.1 The Interconnecting Fabric
  • Parallel SCSI Interface
  • SSA
  • Fibre Channel Topology
  • Other Topologies and Protocols - iSCSI, VI, EtherStorage, InfiniBand
  • Host Bus Adapters
  • Bridges, Routers
  • Hubs
  • Switches
  • FC_AL Storage Switch
  • Directors

2.2 SAN Management Software (SAN Intelligence)
  • Administrative Management
  • Storage Management
  • Storage Resource Management
  • Storage Network Management
  • File Management
  • Where Will the SAN Intelligence Reside?

2.3 The Storage Subsystem
  • Disk Drive Technology
  • Disk Arrays and controllers
  • SAN Appliances
  • SAN Over IP
  • Libraries and Jukeboxes
  • SAN vs. NAS
  • Convergence of SAN & NAS
  • SAN in a Box
  • Roadmap

3. APPLICATIONS

  • Backup and Data Replication
  • Storage Virtualization
  • Clustering
  • Web Serving
  • Storage Utility- Dial Tone
  • E-Commerce

4. THE USER'S VIEW

  • Analysis of end user surveys, as well Service Providers

5. VENDORS and PRODUCTS
Vendors Driving SAN
Partnerships and Alliances
Major SAN and SAN-ready Products, with Product Feature Matrices for:

  • Switches, Hubs, Gateways, ...
  • Management Software
  • Disk Storage Arrays

6. REVENUES AND FORECAST

  • Market Scenarios
  • Switches, Hubs, Gateways, ...
  • Software Management
  • Storage Systems

7. COMPANY PROFILES AND STRATEGIC DIRECTIONS

  • Analysis of the 30 most significant contributors

8. GLOSSARY

Report Objectives

The objective of this report is to analyze the different implementation approaches, compare product functionality, identify the major players, and assess their strategic direction and market shares. The report also forecasts the market evolution.
The report is addressed to marketing managers, planning executives, and system designers from storage system component vendors, integrators, value-added resellers and application service providers. It also addresses Managers of Information Systems and Information Technology personnel responsible for re-architecting their enterprise storage and data management system. The report will also benefit investors and venture capitalists.

This month's Special Report is excerpted from the 2000 Storage Area Network Report
For more information, or to order the report, visit ww.periconcepts.com.

Originally published on .

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