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{zHPF}

Wikipedia talk:Articles for creation/zHPF

The zHPF or z High Performance FICON is a data transfer protocol designed as an extention of the standard FC_SB-3 ^[1] Fibre Channel Protocol. It was announced by IBM on Oct, 2008^[2] and is described in detail in the standard FC-SB-4^[3] of the T11 Technical Committee responsible for Fibre Channel Interfaces.

It was introduced by IBM to improve FICON performances on System z machines. It was designed to substantially improve I/O performance by reducing the number of Channel Command Word (CCWs) and Information Units (sequences) and by removing overhead on the storage subsystem and the FICON channel microprocessor.

To understand how zHPF improves upon FICON, one needs to review the relevant characteristics of FICON channel processing. A FICON channel program consists of a series of Channel Command Words (CCWs) which form a chain. The command code indicates whether the I/O operation is going to be a read or a write from disk and the count field specifies the number of bytes to transfer. When the channel finishes processing one CCW and either a command chaining or data chaining flag is turned on, it processes the next CCW and the CCWs belonging to such a series are said to be chained. Each one of these CCWs is a FICON channel Information Unit (IU) which requires separate processing on the FICON channel processor and separate commands to be sent across the link from the channel to the control unit.

The zHPF architecture defines a single command block to replace a series of FICON CCWs. zHPF improves upon FICON by providing a Transport Control Word (TCW) that facilitates the processing of an I/O request by the channel and the control unit. The TCW has a capability that enables multiple channel commands to be sent to the control unit as a single entity instead of being sent as separate commands as is done with FICON CCWs. In addition, the channel is no longer expected to process and keep track of each individual channel command word. Instead, the channel forwards a chain of commands to the control unit to execute. The reduction of this overhead increases the maximum I/O rate possible on the channel and improves the utilization of the various sub-components along the path traversed by the I/O request.

References

^ T11, "Fibre Channel - Single-Byte Command Code Sets - 3 Mapping Protocol", FC-SB-3 Project
^ IBM, "Announcement Summary", ENUS108-794, October 21, 2008
^ T11, "Fibre Channel - Single-Byte Command Code Sets - 4 Mapping Protocol", FC-SB-4 Project

External links

FC-SB-4 standard FC-SB-4 Project (Technical Committee T11)
z/OS Version 1 Release 11 Implementation (Ch.20) (IBM Redbooks)
z996 and z114 I/O and FICON Express8S Channel Performance (IBM Technical paper)

[1] T11, "Fibre Channel - Single-Byte Command Code Sets - 3 Mapping Protocol", FC-SB-3 Project

[2] IBM, "Announcement Summary", ENUS108-794, October 21, 2008

[3] T11, "Fibre Channel - Single-Byte Command Code Sets - 4 Mapping Protocol", FC-SB-4 Project

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