Models, Methods and Tools for Availability Assessment of IT-Services and Business Processes
Milanovic, Nikola
Die Verfügbarkeit von IT-Services und Geschäftsprozessen ist eine wichtige Voraussetzung für den Erfolg des modernen Geschäfts. Es herrscht die Erwartung dass alle IT-Services auf Knopfdruck und 365 Tage im Jahr Verfügbar sind. Aus diesem Grund stellt die Verfügbarkeit von IT-Services eine kritische Herausforderung dar. Jedoch ist das jetzige Verständnis von Serviceverfügbarkeit zum größten Teil empirisch und ungenau. Die Serviceverfügbarkeit kann oft nur mit einer Mischung von qualitativen (z. B. Interview) und quantitativen (z. B. Messungen) Methoden sehr grob bestimmt werden. Diese Arbeit stellt eine neue Methode vor, welche es ermöglicht die Serviceverfügbarkeit analytisch und modellbasiert zu bestimmen. Der Vorteil dieser Methode ist die Möglichkeit, Serviceverfügbarkeitsmodelle automatisch zu generieren. Dadurch entstehen sehr präzise analytische Werte, welche für die Bestimmung und Testing von Service-Level-Agreements benutzt werden können.
In the world where on-demand and trustworthy service delivery is one of the main preconditions for successful business, service and business process availability is of paramount importance and cannot be compromised. For that reason service availability is in central focus of the IT operations management research and practice. This work presents foundations, models, methods and tools that can be used for comprehensive service and business process availability assessment and management. As many terms in this emerging field are used colloquially, Chapter 2 provides detailed background and definitions. The problem of service availability assessment and management is interdisciplinary, combining fields of fault-tolerance, service oriented architecture and business process management. Another role of this chapter is to make the text accessible to readers with different backgrounds. After the context of service availability has been introduced, Chapter 3 presents existing models for availability and performability assessment. The emphasis is on formal availability models, such as combinatorial (e.g., reliability block diagrams, fault trees) and state-space (e.g., Markov chains, Petri net) models, but qualitative models (e.g., maturity models such as ITIL or CobiT or standards such as ISO 27002 and ISO 12207) are also covered, albeit with limited scope as they are not the primary focus of this work. In Chapter 4, more than 60 commercial, public domain and academic tools for availability assessment are surveyed and compared. Downsides and limitations of standard availability models, both from methodical and practical perspective, are identified and a novel approach for quantitative service availability assessment is presented in Chapter 5. It treats service and process availability as complex functions of availability properties of underlying ICT infrastructure elements and enables automatic generation of availability models, based on service or process description. Finally, Chapter 6 positions presented work in the context of a comprehensive vision for model-based IT service management.
