Following on from the highly-rated FICON 101 webcast. Patty Driever of IBM and Howard Johnson of Broadcom returned for a FICON 201 course which provided a deeper dive into how FICON maps onto the Fibre Channel FC-2 layer, the evolution of the FICON protocol optimizations and how FICON adapts to new technologies.
To help you understand the content of the webinar, we’ve prepared the following Q&A:
Q: What are the characteristics of the mainframe servers that support FICON?
A: Remember this mnemonic: IS FASTER, which stands for Integrity, Security Flexibility, Availability, Serviceability, Transactions, Efficiency and Reliability. Mainframes are built to provide a robust and resilient IT infrastructure, and FICON is a key element in ( their ability to meet the increasing demands placed on reliable and efficient access to data.
Q: How has FICON evolved from its inception?
A: FICON was an evolution from ESCON (Enterprise Systems Connection). Many of the characteristics of ESCON were rigorously evaluated and, in some cases, modified in order to support those characteristics, essentially creating a “FICON state-of-mind” out of Fibre Channel. The first mapping of FICON to the Fibre Channel transport was defined in FC-SB-2, where what’s known as FICON Command Mode, or the original FICON, was first defined. Each subsequent architectural update provided the foundation to support new feature functions such as persistent IU pacing, an FC4 Link Service to aid in discovery and auto-configuration, an extended transport mode for distance support, and more. All of these features helped advance the IS FASTER attributes that uniquely define mainframe servers.
Q: What’s the application of FICON to Fibre Channel?
A: FICON is the adaptation of the System/360 single-byte (SB) architecture to Fibre Channel transports. Parallel interfaces first used SB then ESCON and finally FICON. In the Fibre Channel architecture, this adaptation was originally defined in FC-SB-2 with subsequent revisions adding IU pacing, transport mode, etc. All of these developments improved the IS FASTER attributes of FICON.
Q: What is an Information Unit (IU)?
A: An IU is defined in FC-FS as an organized collection of data that is specified by an upper level to be transferred as a single Sequence by FC-2. What FICON specifies are IUs to pass commands, status, data, control information, or information about unique SB link operations. At the SB-2 layer, these things look like device data frames and the FICON command mode operations use 5 of the SB-2 layer defined information categories, which are specified in the SB-2 header of the frame that is constructed.
Q: What’s involved in building FICON Information Units into Frames?
A: There’s a lot about integrity involved in building or decomposing FICON IUs for transport across a Fibre Channel network. It encompasses what we call “CRCs galore!” CRCs protect the integrity level of the content at each level of data transfer, from a single frame to an IU to the end-to-end data operation. LRC, SB CRC, F2 CRC all play a different role. Suffice it to say, FICON is fanatical about being highly redundant and maintaining high integrity.
Q: How does data transfer work?
A: I/O Operations, (SSCH instructions) are used to transfer data to/from an I/O device or to/from the host main storage. The channel program (CCW chain) guides this data transfer. What’s key to realize is that channels use “real” storage addresses. This means when data is to be placed into or pulled out of contiguous real storage, a single CCW operation is very efficient. But device volumes have grown in capacity over time and virtual memory pages of a host are not likely to be in contiguous real storage, so the chances that the larger amounts of data are likely to be pulled from or placed into contiguous real storage aren’t very high. This requires using multiple CCWs. Alternatively, use of Indirect Data Address Words (IDAWs), Modified Indirect Data Address Words (MIDAWs) and Transport Indirect Data Address Words (TIDAWs) within a CCW can increase the efficiency of sending and receiving large amounts of data.
Q: What is FICON Transport Mode?
A: One of the largest and most recent changes that occurred in FICON was the addition of Transport Mode. The idea is to do more work with one transfer control word. This control word points to a series of commands and associated data, and that’s what’s packaged into IUs so this series can be sent over to the control unit in one or a minimal number of IUs to increase the efficiency on the link.