Bringing Fibre Channel to the Mainframe

In March, IBM will start to deliver new mainframe channel connectivity products based on technology called Fibre Connection (FICON). FICON is a new high-performance I/O interface for Big Iron that supports the characteristics of existing and evolving higher speed access and storage devices.

In a nutshell, FICON products - from IBM and other vendors - will use a new mapping layer that is based on the existing ANSI standard Fibre Channel-Physical and Signaling Interface (FC-PH). FC-PH specifies the physical signaling, cabling and transmission speeds for Fibre Channel.

Each FICON channel is capable of supporting more than 4,000 I/O operations per second, which allows each channel to support the same capacity as up to eight Enterprise Systems Connection (ESCON) channels. FICON channel link speed is 100M byte/sec, compared with 17M byte per second with ESCON links. The full-duplex nature of FICON channels permits them to read and write data concurrently on the same link. IBM is positioning FICON products as a follow-up technology to fiber optic-based ESCON offerings.

FICON products will help customer systems better handle data-intensive workloads and will provide the ability to exploit rapidly evolving device and high-speed link technologies. Technology advances are leading to growth in the data rate capabilities of links and devices, as well as growth in the amount of data stored by a control unit, thus requiring access to more devices. Applications, such as business intelligence, storage-area networks and electronic commerce, benefit from increased data rate and storage capacities because they deal with large data objects and large total amounts of data.

Disaster recovery functions, such as tape vaulting, remote disk copy and geographically dispersed parallel sysplex, which are multiple mainframes strapped together as a single unit, will benefit from the large distance supported by FICON channels. Although direct links between FICON devices of 10 kilometers are supported, 20-kilometer links are possible under certain conditions. The FICON protocol also permits additional end-to-end error checking above that provided by the FC-PH transport.

A FICON channel can operate in native mode or bridge mode. Native mode works with new control unit interfaces and provides the maximum system benefits, such as high end-to-end bandwidth. Bridge mode uses an alternate mapping transports between the FICON channel and a new FICON bridge that supports the attachment of existing ESCON control units to the FICON channel.

From the channel's perspective, both modes exploit the underlying multiplexing capability of Fibre Channel. ESCON supported only one active connected operation and half-duplex data transfer. In contrast, FICON supports multiple active connected operations and full-duplex data transfer.

In native mode, multiple operations may be active on each control unit, as well as across multiple control units. Native mode also supports greater addressability on an individual control unit and greater bandwidth for individual operations.

In bridge mode, ESCON protocols limit activities to one operation per control unit, but multiple control units can be active across the FICON channel. Similarly, there is no increase in bandwidth for any individual control unit because the control units are still on ESCON links; however, there is an increase in addressability (for example, the number of storage devices) that can be communicated with.

In effect, a FICON channel operating in bridge mode acts as a time-division multiplexer, permitting it to do the work of up to eight ESCON channels, even though it is defined as a single channel to the system. In native mode, operation ranges from time-division multiplexing among many operations to a single operation using full bandwidth.

Customer investment in ESCON products is protected in a number of ways. Program compatibility is maintained because I/O operations that worked on ESCON continue to work on FICON. A customer's existing fiber infrastructure can continue to be used, subject to distance constraints of the high-speed technology.

FICON protocols have been streamlined compared with ESCON. Interlocked exchanges have been reduced, improving efficiency and reducing overhead and sensitivity to distance.

FICON is also designed to support a mixed workload: Small data transfers, typical for transactions, do not have to wait for large data transfers to complete.

Instead, they are multiplexed on the link with the long-running operations. This helps to simplify configurations and removes one of the inhibitors to having a single database for transaction processing and business intelligence workloads.

(Meritt is a senior technical staff member with IBM in System/390 System Design, Poughkeepsie, New York. He can be reached at +1 (914) 435-5596 or meritt@us.ibm.com)

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