Support teams of high-performance computing (HPC) systems often find themselves between a rock and a hard place: on one hand, they understandably administrate these large systems in a conservative way, but on the other hand, they try to satisfy their users by deploying up-to-date tool chains as well as libraries and scientific software. HPC system users often have no guarantee that they will be able to reproduce results at a later point in time, even on the same system-software may have been upgraded, removed, or recompiled under their feet, and they have little hope of being able to reproduce the same software environment elsewhere. We present GNU Guix and the functional package management paradigm and show how it can improve reproducibility and sharing among researchers with representative use cases.
Mobile devices (e.g., laptops, PDAs, cell phones) are increasingly relied on but are used in contexts that put them at risk of physical damage, loss or theft. This paper discusses the dependability evaluation of a cooperative backup service for mobile devices. Participating devices leverage encounters with other devices to temporarily replicate critical data. Permanent backups are created when the participating devices are able to access the fixed infrastructure. Several data replication and scattering strategies are presented,including the use of erasure codes. A methodology to model and evaluate them using Petri nets and Markov chains is described. We demonstrate that our cooperative backup service decreases the probability of data loss by a factor up to the ad hoc to Internet connectivity ratio.
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