Hello Lukas,
you know the Task which is runing the command which has to do the IO - it is T128 -
The database console program has additional optionen to get detailed information about what is task T128 doing in detail related to runtime environment.
you can run x_cons <DBNAME> show T_C T128
Option T_C means task details.
May be is should be better to reset all x_cons counters before you start the Join statement again:
x_cons <DBNAME> reset_all
Here you get more information about IO and times.
Additionally you can switch on the command monitor in version 7.9.08.14 you'll get detailed information how many IOs have to be done exactly for this command.
Please start command monitor BEFORE you run the SQL Statement.
Regards, Christiane