Storage

As an IBM mainframe shop, you’ve inevitably encountered the dilemma of migrating from Enterprise System Connection (ESCON) to Fiber Connectivity (FICON) channel. You’ve weighed the pros and cons of this major overhaul, but you’re still undecided whether it’s worth the time, effort, and cost. This article examines why ESCON has been widely adopted in the mainframe world and shows why migrating to FICON is the best choice for your business. At the end of this article, you may ask yourself, “Is 2005 the year for our FICON migration?”

ESCON: A Look Back

ESCON is a marketing name for a set of IBM and vendor products that interconnect S/390 computers with attached storage, locally-attached workstations, and other devices using optical fiber technology and dynamically modifiable switches called ESCON directors. In IBM mainframes, the local interconnection of hardware units is known as channel connection (and sometimes as local   connection to distinguish it from remote or telecommunication connection). ESCON’s fiber-optic cabling can extend this local-to-the-mainframe network up to 60 kilometers (37.3 miles) with chained directors. The data rate on the link itself is up to 200 Mbits/sec and somewhat less when adapted to the channel interface. Vendor enhancements may provide additional distance and higher amounts of throughput.  

In the beginning, ESCON was viewed as a great improvement over its predecessor, bus and tag, where many wires were used to move data simultaneously and in parallel fashion between the mainframe and peripherals. ESCON moved beyond the huge copper cable system bus and tag offered and countered the physical restrictions to offering a serial approach by using optical fiber. Adoption took time as significant testing and proof of concept certifications were conducted. In the end, adoption was primarily driven by the performance improvements ESCON offered.  

Throughout the early ’90s, ESCON eventually replaced much of the bus-and-tag cable and the parallel bit attachment using serial bit-by-bit technology. ESCON, considered the original storage networking technology developed for the mainframe environment, has been installed in most of the world’s data centers. However, it wasn’t long before ESCON was believed to be constrained by its container approach and one-way-at-a-time operation.

The Next Step: FICON

Building on the success of ESCON but incorporating a concurrent approach, FICON is a high-speed I/O interface for mainframe connections to storage devices. As part of IBM’s S/390 server, FICON channels increase I/O capacity through the combination of a new architecture and faster physical link rates to make them up to eight times as efficient as ESCON, IBM’s previous fiber-optic channel standard. This ratio may vary from one installation to the next, and is determined by channel utilization and the mix of peripherals involved on the channel. With the FICON channel, a mapping layer based on the ANSI standard Fibre Channel-Physical and Signaling Interface (FC-PH) specifies the signal, cabling, and transmission speeds. With greater flexibility in terms of network layout, greater distances in bidirectional link rates can be achieved. FICON requires only one channel address and offers full-duplex data transfers, which enables simultaneous reading and writing of data over a single link, and multiplexing, which enables small data transfers to be transmitted with larger ones, rather than having to wait until the larger transaction is finished.  

Based on Fibre Channel (FC), FICON promises far greater connectivity flexibility compared to ESCON. Each FICON channel can support the same capacity as up to eight ESCON channels. FICON is mapped over the Fibre Channel FC-2 protocol layer in both 1GB/second and 2GB/second implementations. Within the FC standard, FICON is defined as a level-4 protocol called SB-2, which is the generic terminology for IBM’s single-byte command architecture for attached I/O devices. FICON and SB-2 are interchangeable terms; it’s a connectionless point-to-point or switched point-to-point FC topology. FICON can support multiple concurrent data transfers and full-duplex channel operations (multiple simultaneous reads and writes), compared to the half-duplex operation of ESCON.  

FICON is an I/O protocol used between IBM (and compatible) mainframes and storage arrays. FICON takes the higher-layer ESCON protocol, analogous to SCSI, and maps it onto an FC transport. FC is the dominant technology used today in storage networks for open systems. FICON takes ESCON to the next level. FICON’s ability to multiplex multiple channel programs is like being able to send many messages in different containers in both directions simultaneously. It’s a compelling technology and there are many enterprises that have been waiting to install it and reap the rewards. For others, it’s important to look beyond the technological justification and to determine how best to implement the FICON technology to maximize ROI.  

With FICON, history has repeated itself. Launched by IBM on S/390 in 1997, it was clearly a technically superior product. For almost four years, the only devices that would connect via FICON   were tape drives (an important improvement for backup and recovery) and printers. Only in 2001 did IBM finally add FICON connectivity to its enterprise storage server (a.k.a. “Shark”). But there are significant differences this time around, and there was an accelerated rate of FICON adoption in 2002.  

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