SPD cabling

During a model upgrade or an expansion unit conversion of a partitioned system (moving a partition from one server to another or changing an expansion unit from a 5065 to a 5074), an SPD bus may be removed.

This has serious consequences to the LPAR configuration. SPD buses are cabled in pairs and are numbered by the system on each IPL. This numbering is done by determining to which port they are connected from the bus adapter. When there are two buses connected to a bus adapter, the numbering of the buses is determined as follows. A cable runs from the top port of the bus adapter to the top port of the SPD bus; this is the first bus number. A cable then runs from the bottom port of the SPD bus to the top port of the second SPD bus; this is the next bus number. Finally, a cable runs back to the system to complete the loop.

Due to the way these buses are cabled, they always have the same bus number on each IPL. However, if the first bus is removed, the second bus takes the bus number of the first bus. If both of these buses are in the same partition, required LPAR configuration actions are minimal. If the hardware in these buses is spread between different partitions or if there is a required resource, for instance load source or console, LPAR configuration actions must be taken before the partitions are powered on. The following step should be performed any time an SPD bus is removed from a partitioned system:

Determine if the bus to be removed will result in another bus being renumbered.

Use the following table to determine if the bus that will be removed is cabled to the top or bottom port of the bus expansion adapter.
If the bus being removed is cabled to the bottom port of the bus expansion adapter, then no buses are being recabled due to the conversion of this tower.
If the bus being removed is cabled to the top port of the bus expansion adapter, then determine if there is also a bus attached to the bottom port (it will be one number higher than the bus being removed). If there is a bus attached to the bottom port of the bus expansion adapter, then there will be a bus recabled during this expansion unit conversion.

iSeries™ server model	Bus numbers
iSeries™ server model	Top port	Bottom port
720/620	Odd	Even
730/740/SX0	Even	Odd
820/830/840*	Odd	Even

* Only applies to buses 5 through 22.

Example: If bus 10 is to be removed on an iSeries Model 730 server, then bus 10 is cabled to the top port ("even" buses on an iSeries Model 730 server are attached to the top port) so the system must be checked to determine whether a bus 11 is present.