The HiperSockets™ hardware supports four different frame sizes referred to as the HiperSockets MFS (maximum frame size). Using HCD (or IOCP), the HiperSockets MFS is configured on the IQD CHPID using the 'OS=' parameter. All LPARs communicating over the same IQD CHPID will then use the same IQD MFS. The MFS affects the largest packet that TCP/IP can transmit. TCP/IP will adjust the MTU (Maximum Transmission Unit) based on the MFS, which is discovered during activation.
| OS=value | HiperSockets frame size | TCP/IP MTU size |
|---|---|---|
| 00 (default) | 16 KB | 8 KB |
| 40 | 24 KB | 16 KB |
| 80 | 40 KB | 32 KB |
| C0 | 64 KB | 56 KB |
The default HiperSockets MFS is 16 KB. However, in cases in which increased bandwidth is required (such as large file transfers, file backup), a larger MFS could be used. In most workload environments the default size will result in better storage and CPU usage.
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* OS values are '00'=16K, '40'=24K, '80'=40K and 'C0'=64K. *
* *
* Need at least 3 addresses per z/OS, maximum of 10: *
* - 2 addresses for control *
* - 1 address for data for each TCP stack (between 1 and 8) *
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ID SYSTEM=(2064,1)
*
CHPID PATH=FC,TYPE=IQD,SHARED,OS=00
CHPID PATH=FD,TYPE=IQD,SHARED,OS=40
CHPID PATH=FE,TYPE=IQD,SHARED,OS=80
CHPID PATH=FF,TYPE=IQD,SHARED,OS=C0
*
CNTLUNIT CUNUMBR=FC00,PATH=FC,UNIT=IQD
IODEVICE ADDRESS=(2C00,16),CUNUMBR=FC00,UNIT=IQD
*
CNTLUNIT CUNUMBR=FD00,PATH=FD,UNIT=IQD
IODEVICE ADDRESS=(2C10,16),CUNUMBR=FD00,UNIT=IQD
*
CNTLUNIT CUNUMBR=FE00,PATH=FE,UNIT=IQD
IODEVICE ADDRESS=(2C20,16),CUNUMBR=FE00,UNIT=IQD
*
CNTLUNIT CUNUMBR=FF00,PATH=FF,UNIT=IQD
IODEVICE ADDRESS=(2C30,16),CUNUMBR=FF00,UNIT=IQD See z/OS HCD Planning and Using HCD for additional details.