High Performance FICON for System Z Technical Summary for Customer Planning
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January 2009 High Performance FICON for System z Technical summary for customer planning Iain Neville System z Consulting IT specialist IBM Systems and Technology Group IBM United Kingdom System z High Performance FICON customer readiness documentation Page 1 Table of Contents Who should read this document? .................................................................................................................2 What is the purpose of this document? ........................................................................................................2 Overview of System z High Performance FICON .........................................................................................2 Mainframe I/O technology milestones: ESCON to zHPF ..............................................................................3 ESCON architecture..................................................................................................................................3 FICON architecture ...................................................................................................................................4 MIDAW facility........................................................................................................................................5 High Performance FICON for System z (zHPF) ........................................................................................6 RAS benefits with zHPF .........................................................................................................................8 zHPF Frequently Asked Questions........................................................................................................8 References..................................................................................................................................................14 Acknowledgements ....................................................................................................................................14 System z High Performance FICON customer readiness documentation Page 2 Who should read this document? This document should be referenced by IBM System z® hardware planners, system programmers and those with responsibility for the technical positioning of the System z platform. What is the purpose of this document? This document provides the following: A high level overview of High Performance FICON for System z (zHPF) to give the reader an understanding of the significance of the enhancements to the z/Architecture® and FICON® interface architecture to increase performance for online transaction processing workloads. At a high level, demonstrate the value of the zHPF architecture. List the high level pre-requisites for the adoption of zHPF. A list of answers for a set of frequently asked questions. Overview of System z High Performance FICON High Performance FICON for System z (zHPF) is one of IBM’s latest enhancements to the z/Architecture and FICON interface architecture to dramatically improve the performance of OLTP workloads. These architectural enhancements are designed to substantially improve I/O performance by reducing the number of Channel Command Words (CCWs) and Information Units (sequences) which remove overhead on the storage subsystem and the FICON channel microprocessor. The rationalization of layers of handshakes is established without compromising the reliability, availability and serviceability (RAS) implemented with FICON technology today. These enhancements have been for optimization of online transaction processing (OLTP) workloads using numerous access methods such as DB2®, VSAM, PDSE, HFS, zFS. When exploited by the FICON channel, the z/OS® operating system, and the storage subsystem, zHPF is designed to help reduce overhead and improve performance. Additionally, the changes to the architectures offer end-to-end system enhancements to improve reliability, availability, and serviceability (RAS). System z High Performance FICON customer readiness documentation Page 3 Mainframe I/O technology milestones: ESCON to zHPF The evolution of mainframe I/O architecture includes many significant milestones. When these are reviewed from the outset, the significance of zHPF can be put into context. In particular when we compare a start I/O using ESCON® to that of FICON and now zHPF, the significance of these iterative changes becomes apparent. A brief summary of the differences between ESCON architecture and FICON and zHPF architecture is captured in Table 1. ESCON Native FICON, CTC, zHPF Circuit switching Packet switching Read or write Simultaneous read and write Half-duplex data transfers Full-duplex data transfers Connection-oriented Connectionless Pre-established Packets dedicated path individually routed Connection is locked Connection released when data sent when data sent Synchronous transfers Asynchronous transfers CCW architecture CCW architecture for FICON TCW architecture for zHPF Table 1: Channel Architecture comparisons ESCON architecture Enterprise Systems Connection (ESCON) is a 17MBps architecture first introduced in September 1990. This is a circuit switching architecture that mandates a channel end and device end (CE/DE) is received for every CCW (command) before the channel is released. ESCON is industry standard – Single Byte Command Code Sets Connection Architecture (SBCON). System z High Performance FICON customer readiness documentation Page 4 ESCON command and data sequences: 4 x 4K reads. Device ESCON Channel Storage subsystem Control Unit CCW1 Read 4K CCW1 CCW1 CE/DE END CCW2 Read 4K CCW2 CCW2 CE/DE END CCW3 Read 4K CCW3 CCW3 CE/DE END CCW4 Read 4K CCW4 CCW4 CE/DE END • Each CCW is individual and traverses the link in a serial manner. • Channel End (CE) and Device End (DE) for each CCW Figure 1: ESCON command and data sequences Figure 1 shows 4 CCWs being executed. A channel end / device end must be received before another can be executed. FICON architecture Fibre Connection (FICON) is a packet switching architecture that scales from 1Gbps to 10 Gbps and was first made available in August 1999. FICON creates a logical end to a chain of CCWs. There is no longer a requirement to wait for an individual channel and device end (CE/DE). A logical end is established to the control unit after each CCW is executed. FICON is also industry standard – Fibre Channel Single Byte Command Code Sets-3 (FC-SB-3). Information Units (IUs or sequences) of up to 8K in size are built for each CCW. Each IU is then split into frames of 2K which are formatted individually before being sent over the optic link as reflected in Figure 2. System z High Performance FICON customer readiness documentation Page 5 FICON command and data sequences: 4 x 4K reads FICON Channel Storage subsystem Device Control Unit CMR CMD Prefix +64 CCW1 CCW1 Read 4K CCW1 Data 4K CCW2 Read 4K CCW2 We no CCW3 Read 4K CCW3 CCW2 longer CCW4 Read 4K CCW4 Data 4K have to CCW3 Data 4K wait….. CCW4 Data 4K CE / DE Status Status Accept Note: standard CCWs, not Read track Data Figure 2: FICON command and data sequences The picture above is simplified. With Extended Format (EF) datasets each CCW (command) from the channel adds a 32 byte suffix to each command and data block. This requires an additional 4 x IUs to build into the command sequence and a corresponding 4 x IUs for the data stream coming back from the storage subsystem. Over time there have been a number of enhancements to improve performance in a FICON environment. MIDAW facility The Modified Indirect Data Address Word (MIDAW) facility was introduced in July 2005. This enhancement implements an extension to indirect addressing to improve performance by rationalizing the number of CCWs. The restriction of aligning the data to a page boundary is removed. This facility benefits applications using numerous dataset types including Extended Format datasets, VSAM, PDSEs and zFS. The suffix now becomes a different address (MIDAW) to the same CCW, reducing the number of command sequences by up to 46%. System z High Performance FICON customer readiness documentation Page 6 MIDAW: 2 CCWs reading 14 Extended Format (EF) disk records CCW #1: Write Prefix CC Count=64 4K CCW #2: Read Track Data M Count=57792 Addr=1A000000 buffer CC = Command Chaining 4K M = MIDAL indicator buffer MIDAW #1: Flag=00 Count=4096 Addr=20000000 ... MIDAW #2: Flag=00 Count=32 Addr=1E000000 MIDAW #3: Flag=00 Count=4096 Addr=25000000 4K MIDAW #4: Flag=00 Count=32 Addr=1E000020 buffer . 1st record suffix . 2nd record suffix . MIDAW #27: Flag=00 Count=4096 Addr=31000000 . MIDAW #28: Flag=L Count=32 Addr=1E0001A0 . L = Last MIDAW indicator 14th record suffix Figure 3: MIDAW facility and chained CCWs With MIDAWs a sequence of chained CCWs can effectively be reduced to two within a limit of 64K. Figure 3 reflects this with an entire track of 4K reads being reduced from fourteen CCWs down to two. However, the data blocks from the storage subsystem are still transferred individually back to memory. High Performance FICON for System z (zHPF) With the introduction of zHPF, the FICON architecture has been streamlined by removing significant overhead to the storage subsystem and the microprocessor within the FICON channel. A command block is created to chain commands into significantly fewer IUs. The overhead required to convert individual commands into FICON format is removed as multiple System z I/O commands are packaged together and passed directly over the fibre optic link. For zHPF operations, we lose the concept of the Command Control Word (CCW). This