Storage area networking - emerging data communications platform promising to eliminate bandwidth bottlenecks, scalability limitations associated with SCSI architectures - Technology Information

A look at the network behind the server.

The storage area network (SAN) is an emerging data communications platform that interconnects servers and storage at gigabaud speeds. By combining LAN networking models with the core building blocks of server performance and mass storage capacity, SANs may eliminate the bandwidth bottlenecks and scalability limitations imposed by previous SCSI bus-based architectures.

The SAN networking approach facilitates computer clustering, topological flexibility, fault tolerance, high availability, and remote management. From a client network perspective, the SAN environment complements the ongoing advancements in LAN and WAN technologies by extending the benefits of improved performance and capabilities all the way from the client and backbone through to servers and storage.

THE OPEN SAN SOLUTION

Over the past year, Fibre Channel-arbitrated loop (FC-AL) has emerged as the high-speed, serial technology of choice for server-storage connectivity. With more than 70 companies--including industry-leading disk drive, disk array, server, and networking connectivity suppliers--supporting FC-AL, it has become the most widely endorsed open standard for the SAN environment. This broad acceptance is attributed not only to FC-AL's high bandwidth and high scalability but also to its unique ability to support multiple protocols, such as SCSI and IP, over a single physical connection. This enables the SAN infrastructure to serve as both a server interconnect and as a direct interface to storage devices and storage arrays.

FC-AL provides a 2.5- to 10-fold increase in effective data bandwidth over the traditional parallel SCSI storage interface. Additionally, FC-AL offers future expandability. While the current FC-AL standard for bandwidth is 1 gigabaud, planned enhancements to 2 and 4 gigabaud give FC-AL a solid platform to address longer-term bandwidth requirements.

The modular scalability of FC-AL is key to long-term growth and manageability. Traditional parallel SCSI bus connections have been limited to a total of 7 or 15 storage devices. As bus bandwidth is pushed further and further, this limit is compressed to even fewer devices per bus. In contrast, FC-AL supports up to 126 nodes per loop with a typical configuration consisting of a combination of servers and multi-disk arrays per node. By adding multiple loops, the overall scalability is limitless.

Scalability in terms of capacity management and capacity balancing is an area of significant differentiation between FC-AL and SCSI. Largely dictated by the limits on physical cable length, parallel SCSI storage connectivity requires close proximity to its host system, typically a server. This translates to a single, integrated server-storage enclosure that contains both server processing power and one or two SCSI buses of limited scalability.

MODULAR CONNECTIVITY

In addition to superior flexibility in scaling server processing capacity and data storage capacity, the networking approach of FC-AL introduces aspects of interconnect scalability that have not been possible with previous architectures. Through the use of modular networking devices such as hubs, switches, bridges and routers, advanced SAN topologies can be created to scale overall bandwidth, enhance availability, and enable advanced SAN application capabilities in storage management and load balancing.

Many FC-AL devices provide features that ease the general deployment of fault-tolerant SANs such as dual porting, which has become standard on FC-AL disk drives. Dual loop configurations provide a redundant path to each storage device in the array in the event that one of the loops is down or busy.

The redundant array of independent disks (RAID) in storage arrays has become a standard approach for fault tolerance and is fully supported by the SAN environment. In fact, FC-AL disk drives provide internal exclusive-or (XOR) logic which effectively provides Level 5 RAID capabilities from within the disk drive itself. This addition facilitates robust, proven fault tolerance while reducing the requirement for more complex and costly RAID controllers.

Visibility down to the node and device level is essential to easing the efforts of installation, deployment, and maintenance of any network. By embracing a network management approach, SAN connectivity devices, such as hubs and switches, have integrated highly evolved management capabilities modeled after proven LAN and WAN management techniques. A fully managed SAN platform can offer monitoring and bypass control of individual nodes, loops, enclosures, storage devices, and connectivity devices.

EASE OF INTEGRATION

Since the SAN environment exists behind the server, existing server-LAN connections can easily be leveraged to facilitate a gateway between LAN and SAN, and allow utilization of legacy servers.

The broad cabling options supported by FC-AL also ease the introduction of SANs into existing campus networks. By leveraging pre-existing twisted pair, coax, and optical cabling, SAN connection distances of up to 10 km can be achieved without the need to pull new cable.

SAN connectivity devices offer dynamically configurable, hot-plugging capabilities. Combined with a graphical management interface, these features simplify troubleshooting and accelerate installation.

Offering an infrastructure for cost-effective, long-term growth, fault tolerance and manageability, the SAN environment provides new total cost of ownership (TCO) advantages.

Tang is the director of business development at Gadzoox Microsystems, Inc., San Jose, Calif.

Complementary SAN, LAN and WAN Technologies

Technology  Current Bandwidth   Future Bandwidth   Applications

ATM            622 Mbps            1+ Gbps           LAN and WAN
Ethernet       100 Mbps            1 Gbps            LAN and WAN
FC-AL          1 Gbps              4 Gbps                SAN

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