Predicting Intermediate Storage Performance for Workflow Applications

Configuring a storage system to better serve an application is a challenging task complicated by a multidimensional, discrete configuration space and the high cost of space exploration (e.g., by running the application with different storage configurations). To enable selecting the best configuration in a reasonable time, we design an end-to-end performance prediction mechanism that estimates the turn-around time of an application using storage system under a given configuration. This approach focuses on a generic object-based storage system design, supports exploring the impact of optimizations targeting workflow applications (e.g., various data placement schemes) in addition to other, more traditional, configuration knobs (e.g., stripe size or replication level), and models the system operation at data-chunk and control message level. This paper presents our experience to date with designing and using this prediction mechanism. We evaluate this mechanism using micro- as well as synthetic benchmarks mimicking real workflow applications, and a real application.. A preliminary evaluation shows that we are on a good track to meet our objectives: it can scale to model a workflow application run on an entire cluster while offering an over 200x speedup factor (normalized by resource) compared to running the actual application, and can achieve, in the limited number of scenarios we study, a prediction accuracy that enables identifying the best storage system configuration

Towards Multi-site Metadata Management for Geographically Distributed Cloud Workflows

International audienceWith their globally distributed datacenters, clouds now provide an opportunity to run complex large-scale applications on dynamically provisioned, networked and federated infrastructures. However, there is a lack of tools supporting data-intensive applications across geographically distributed sites. For instance, scientific workflows which handle many small files can easily saturate state-of-the-art distributed filesystems based on centralized metadata servers (e.g. HDFS, PVFS). In this paper, we explore several alternative design strategies to efficiently support the execution of existing workflow engines across multi-site clouds, by reducing the cost of metadata operations. These strategies leverage workflow semantics in a 2-level metadata partitioning hierarchy that combines distribution and replication. The system was validated on the Microsoft Azure cloud across 4 EU and US datacenters. The experiments were conducted on 128 nodes using synthetic benchmarks and real-life applications. We observe as much as 28% gain in execution time for a parallel, geo-distributed real-world application (Montage) and up to 50% for a metadata-intensive synthetic benchmark, compared to a baseline centralized configuration