Stephan Kraft

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We propose a linear regression method and a maximum likelihood technique for estimating the service demands of requests based on measurement of their response times instead of their CPU utilization. Our approach does not require server instrumentation or sampling, thus simplifying the parameterization of performance models. The benefit of this approach is(More)
We propose simple models to predict the performance degradation of disk requests due to storage device contention in consolidated virtualized environments. Model parameters can be deduced from measurements obtained inside Virtual Machines (VMs) from a system where a single VM accesses a remote storage server. The parameterized model can then be used to(More)
Within the scope of the European research and education network project GEANT2, including a framework for performance measurements, the need for statistical analysis and interpretation of network performance metrics has to be satisfied. Following the IETF approach, a measurement system for metrics as one-way-delay (OWD), OWD-variation (OWDV) and packet loss(More)
In this paper, we propose simple performance models to predict the impact of consolidation on the storage I/O performance of virtualized applications. We use a measurement-based approach based on tools such as blktrace and tshark for storage workload characterization in a commercial virtualized solution, namely VMware ESX server. Our approach allows a(More)
Analytic performance models are being increasingly used to support system runtime optimization. This paper considers the modelling features needed to predict the response time behaviour of an industrial enterprise resource planning (ERP) application, SAP ERP. A number of studies have reported modelling success with the application of basic product-form(More)
We report on new charge calibrations and linearity tests with high-dynamic range for eight different scintillating screens typically used for the detection of relativistic electrons from laser-plasma based acceleration schemes. The absolute charge calibration was done with picosecond electron bunches at the ELBE linear accelerator in Dresden. The lower(More)
 Twenty-four-hour ambulatory blood pressure monitoring (ABPM) has many advantages for the diagnosis and follow-up of hypertension at all ages. This technique has so far not been documented as applicable to the very young. We studied the feasibility of ABPM in 61 healthy children and in 40 patients with renal diseases and/or hypertension, aged less than 6(More)
Wir berichten über ein 3jähriges Mädchen, das wegen statomotorischer und mentaler Retardierung, generalisierter Muskelhypotonie und übermäßigem Wachstum zur klinisch-genetischen Diagnostik kam. Zytogenetisch wurde eine De-novo-Deletion 22q13 festgestellt. In der Literatur wurden 7 Patienten mit einem ähnlichen Phänotyp beschrieben. Diskussion: Es ist zu(More)
Popliteal synovial cysts (Baker’s cysts) are a common occurrence in children and adults. Synovial cysts in other locations and/or with atypical extension are less common and may be confounded with tumors or other medical conditions. In this article we describe the underlying disease, clinical presentation and clinical course in six children with a sudden(More)
We propose a trace-driven approach to predict the performance degradation of disk request response times due to storage device contention in consolidated virtualized environments. Our performance model evaluates a queueing network with fair share scheduling using trace-driven simulation. The model parameters can be deduced from measurements obtained inside(More)