The newly developed parallel Input/Output-libray SIONlib is applied to the highly scalable parallel multiscale code MP2C, which couples a mesoscopic fluid method based on multi-particle collision dynamics to molecular dynamics. It is demonstrated that for fluid-benchmark systems, a significant improvement of scalability under production conditions can be achieved. It is shown that for the BlueGene/P architecture at Jülich a performance close to the bandwidth capacity of 4.7 GByte/sec can be obtained. The article discusses the ease of use of SIONlib from the point of view of application.