Some applications are constrained by today's 1Gbps/2Gbps Fibre Channel SANs, and 4Gbps, 8Gbps, or 10Gbps connections may be the answer.
By Ravi Prakash
"If my petabytes of storage and thousands of SAN ports don't saturate my 2Gbps Fibre Channel links, why do I need 4Gbps or, for that matter, 8Gbps or 10Gbps, Fibre Channel?"
The above question is typically asked by SAN administrators who wonder whether the need for more speed really exists or whether it is just something hyped by vendors wanting to sell more cutting-edge hardware. This article explores applications for Fibre Channel SANs that go beyond today's 1Gbps and 2Gbps speeds.
In the video-editing industry, raw uncompressed HDTV files are usually transported over Fibre Channel for editing purposes. A typical post-production studio has a person using real-time HD editing software to edit video on a graphics workstation equipped with a Fibre Channel HBA that supports one or two 2Gbps Fibre Channel ports. In this application, one editor could be adding or correcting colors to the video while another might be adding titles, both using cluster file-system software. Many terabytes of video content could reside on a shared RAID array, which is accessed by many editing workstations over the Fibre Channel SAN. The workstations may need access to multiple streams of HDTV content.
A progressive scan non-interlaced HDTV sequence has 720 lines of 1,280 pixels. If the frame rate is 60 frames per second the data rate will be about 165MBps. Today's 2Gbps Fibre Channel HBA ports typically offer a bandwidth of just 212MBps, which is barely adequate for a single HDTV stream. On the horizon, however, there are new formats for HDTV, such as Sony's HD CAM SR, which uses 240MBps for a single video stream. For these applications the higher data rate of 800MBps offered by dual-port 4Gbps Fibre Channel provides a better SAN infrastructure.
Keep in mind that merely having 4Gbps bandwidth on an HBA is not enough. To make optimal use of this doubled bandwidth, the server bus should be PCI Express or PCI-X 2.0, rather than PCI or PCI-X.
This example illustrates just one of numerous applications that can benefit from using 4Gbps Fibre Channel, which delivers twice the bandwidth of 2Gbps Fibre Channel. Other examples can be found in the oil and gas industries where a company may generate 1TB to 2TB of raw data from a seismic analysis application and then pass this on to a data processing and imaging services company that could be dealing with data sets in the 3TB to 7TB range. These requirements tax a multi-terabyte 2Gbps Fibre Channel RAID system. Other applications that could benefit from 4Gbps Fibre Channel include the following:
Transaction processing-One example is online retailers that offer product catalogs with multimedia.
Streaming applications-These applications deliver digital audio, video, data, and MPEG-2 in real time.
LAN-free backup-Backing up data from disk arrays to tape libraries in block format over a high-speed SAN fabric allows backups to proceed without any adverse impact on the production LAN.
Optical libraries are another form of storage that may benefit from the higher bandwidth provided by 4Gbps Fibre Channel. New optical libraries use RAID architectures to stripe data across multiple DVD-RAM or magneto-optical (MO) drives in a single library. These libraries may be used for backup applications, instead of tape. Moving massive amounts of data using much larger block sizes would place severe strain on a 2Gbps Fibre Channel infrastructure.
Other benefits of 4Gbps Fibre Channel include
- Backward-compatibility with existing 1Gbps and 2Gbps Fibre Channel products and infrastructure;
- The same encoding scheme, connectors, and cables used in 1Gbps/2Gbps Fibre Channel;
- Auto-negotiation, which detects the supported speed and adjusts appropriately without user intervention; and
- About the same price as 2Gbps Fibre Channel products.
4Gbps Fibre Channel will be supported by system, disk array, HBA, switch, enclosure, cable, and component suppliers. With its backward-compatibility and low cost, 4Gbps Fibre Channel will ensure seamless SAN migration while preserving current investments.
In addition, improvements in disk density and rotation rates means that disk arrays can now deliver burst rates exceeding 200MBps, saturating the bandwidth of 2Gbps Fibre Channel. This will drive adoption of 4Gbps Fibre Channel, and eventually 8Gbps Fibre Channel (which is expected in the 2008 time frame), inside disk arrays between controllers and drives.
Today, the primary application for 10Gbps Fibre Channel is in inter-switch links (ISLs) interconnecting SAN switches at the core of a fabric. In a SAN switch with 2Gbps Fibre Channel ports dedicated to ISLs, the
2Gbps ports can create a bottleneck. Some switch vendors provide ways to trunk 2Gbps ISL ports into logical "fat pipes" with load balancing to form a virtual pipe that simulates a physical 10Gbps fat pipe. An alternative is to use native 10Gbps ports for ISLs, which are available on some SAN switches. These ports are dedicated to inter-switch connectivity, eliminating the need to use 2Gbps ports for 10Gbps trunking. This allows users to achieve more-efficient use of switch hardware and associated infrastructure because all of the existing 2Gbps ports are freed up for server/storage connectivity.
Today's 2Gbps Fibre Channel technology is sufficient for most SAN applications. However, advancements in server buses, disk drive speeds, and other factors will drive adoption of 4Gbps Fibre Channel over the next few years. Expected late this decade, 8Gbps Fibre Channel will be targeted at the edge of the SAN for backward-compatible migration from 4Gbps Fibre Channel. It is also expected that 8Gbps Fibre Channel will be used within disk arrays and for inter-connecting disk arrays to tape libraries.
Ravi Prakash is the outbound marketing manager at QLogic Corp. This article was reviewed by the Fibre Channel Industry Association (www.fibrechannel.org).