Also, the changes to the architectures provide end-to-end system enhancements to improve reliability, availability, and serviceability (RAS). 

zHPF is compatible with the following standards: 

GLYPH<SM590000> Fibre Channel Framing and Signaling standard (FC-FS) 

GLYPH<SM590000> Fibre Channel Switch Fabric and Switch Control Requirements (FC-SW) 

GLYPH<SM590000> Fibre Channel Single-Byte-4 (FC-SB-4) standards 

For example, the zHPF channel programs can be used by the z/OS OLTP I/O workloads, Db2, VSAM, the partitioned data set extended (PDSE), and the z/OS file system (zFS). 

At the zHPF announcement, zHPF supported the transfer of small blocks of fixed size data (4 K) from a single track. This capability was extended, first to 64 KB, and then to multitrack operations. The 64 KB data transfer limit on multitrack operations was removed by z196. This improvement allows the channel to fully use the bandwidth of FICON channels, which results in higher throughputs and lower response times. 

The multitrack operations extension applies exclusively to the FICON Express16S+, FICON Express16S, and FICON Express8S, on the z14 M0x, z14 ZR1, z13, z13s, zEC12, and zBC12, when configured as CHPID type FC and connecting to z/OS. zHPF requires matching support by the DS8000 series. Otherwise, the extended multitrack support is transparent to the control unit. 

zHPF is enhanced to allow all large write operations (greater than 64 KB) at distances up to 100 kilometers (62.13 miles) to be run in a single round trip to the control unit. This process does not increase the I/O service time for these write operations at extended distances. This enhancement to zHPF removes a key inhibitor for clients that are adopting zHPF over extended distances, especially when the IBM HyperSwap capability of z/OS is used. 

From the z/OS perspective, the FICON architecture is known as command mode  and the zHPF architecture is known as transport mode . During link initialization, the channel node and the control unit node indicate whether they support zHPF. 

Requirement:  All FICON channel path identifiers (CHPIDs) that are defined to the same LCU must support zHPF. The inclusion of any non-compliant zHPF features in the path group causes the entire path group to support command mode only. 

The mode that is used for an I/O operation depends on the control unit that supports zHPF and its settings in the z/OS operating system. For z/OS use, a parameter is available in the IECIOSxx member of SYS1.PARMLIB ( ZHPF=YES  or NO ) and in the SETIOS  system command to control whether zHPF is enabled or disabled. The default is ZHPF=NO . 

Support is also added for the D IOS,ZHPF  system command to indicate whether zHPF is enabled, disabled, or not supported on the server. 

Similar to the existing FICON channel architecture, the application or access method provides the channel program (CCWs). How zHPF (transport mode) manages channel program operations is different from the CCW operation for the existing FICON architecture (command mode). 

While in command mode, each CCW is sent to the control unit for execution. In transport mode, multiple channel commands are packaged together and sent over the link to the control unit in a single control block. Fewer processors are used compared to the existing FICON architecture. Certain complex CCW chains are not supported by zHPF. 

