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IBM Journal of Research and Development  
Volume 51, Number 1/2, Page 173 (2007)
IBM System z9
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Redundant I/O interconnect

by U. Helmich, M. Becht, M.J. Becht, J.R. Easton, R.K. Errickson, T. Gehrmann, S.G. Glassen, S.R. Greenspan, F. Koeble, H. Lehmann, C. Mayer, J.S. Nikfarjam, F.A. Schumacher, W. Storz
The outstanding reliability, availability, and serviceability (RAS) characteristics of IBM mainframe computers are among the features that gained the IBM eServer™ family its reputation as a leading platform for business-critical applications. The aim now is to further improve IBM System z9® RAS by introducing redundant I/O interconnect (RII) as a building block of enhanced book availability and recovery scenarios. RII provides a means of maintaining I/O connectivity during planned or unplanned outages in a way that is transparent to the operating system and customer applications. The mechanism that meets this requirement is the provision of an alternate path to the I/O cage, which provides high-bandwidth I/O slots to enable a higher number of I/O ports per card. This paper discusses the I/O subsystem hardware and firmware aspects of RII.
Related Subjects: Channel subsystem architecture; IBM System z9; Packaging; Reliability