Jean Araujo

An availability model for eucalyptus platform: An analysis of warm-standy replication mechanism

High availability in cloud computing services is essential for maintaining customer confidence and avoiding revenue losses due to SLA violation penalties. Since the software and hardware components of cloud infrastructures may have limited reliability, fault tolerance mechanisms are a means of achieving the necessary dependability requirements. This paper investigates the benefits of a warm-standy replication mechanism in a Eucalyptus cloud computing environment. A hierarchical heterogeneous modeling approach is used to represent a redundant architecture and compare its availability to that of a non-redundant architecture. Both hardware and software failures are considered in the proposed analytical models. The results show an enhanced dependability for the proposed redundant system, as well as a decrease in the annual downtime. The results also demonstrate that the simple replacement of hardware by more reliable machines would not produce improvements in system availability to the same extent as would the fault tolerant approach.

Experimental evaluation of software aging effects on the eucalyptus cloud computing infrastructure

The need for reliability and availability has increased in modern applications, which need to handle rapidly growing demands while providing uninterrupted service. This work investigates the memory leak and memory fragmentation aging effects on the Eucalyptus cloud-computing framework, which considers workloads composed of intensive requests addressing different virtual machines. We experimentally show the existence of the investigated aging effects in the cloud environment under study. Also, a software rejuvenation strategy to mitigate the observed aging effects is proposed and its benefits are evaluated.

Software aging issues on the eucalyptus cloud computing infrastructure

Demands on software reliability and availability have increased due to the nature of present day applications. Cloud computing systems fundamentally provide access to large pools of data and computational resources through a variety of interfaces similarly to existing grid and HPC resource management and programming systems. This work investigates the software aging effects on the Eucalyptus cloud computing infrastructure considering workloads composed of provisioning different types of virtual machines.

Availability study on cloud computing environments: Live migration as a rejuvenation mechanism

With the increasing adoption of cloud computing environments, studies about high availability in those systems became more and more significant. Software rejuvenation is an important mechanism to improve system availability. This paper presents a comprehensive availability model to evaluate the utilization of the live migration mechanism to enable VMM rejuvenation with minimum service interruption. Live migrations are performed observing a time-based trigger. We evaluate five different scenarios, with distinct time intervals for triggering the rejuvenation. The results show that the live migration can significantly reduce the system downtime.

Software Rejuvenation in Eucalyptus Cloud Computing Infrastructure: A Method Based on Time Series Forecasting and Multiple Thresholds

The need for reliability and availability has increased in modern applications, in order to handle rapidly growing demands while providing uninterrupted service. Cloud computing systems fundamentally provide access to large pools of data and computational resources through a variety of interfaces similarly to existing grid and HPC resource management and programming systems. This work proposes an approach that uses time series to schedule rejuvenation, so as to reduce the downtime by predicting the proper moment to perform the rejuvenation.We show the results of our approach through experiments using the Eucalyptus cloud computing framework.

Sensitivity analysis of a hierarchical model of mobile cloud computing

Abstract Mobile cloud computing is a new paradigm that uses cloud computing resources to overcome the limitations of mobile computing. Due to its complexity, dependability and performance studies of mobile clouds may require composite modeling techniques, using distinct models for each subsystem and combining state-based and non-state-based formalisms. This paper uses hierarchical modeling and four different sensitivity analysis techniques to determine the parameters that cause the greatest impact on the availability of a mobile cloud. The results show that distinct approaches provide similar results regarding the sensitivity ranking, with specific exceptions. A combined evaluation indicates that system availability may be improved effectively by focusing on a reduced set of factors that produce large variation on the measure of interest. The time needed to replace a fully discharged battery in the mobile device is a parameter with high impact on steady-state availability, as well as the coverage factor for the failures of some cloud servers. This paper also shows that a sensitivity analysis through partial derivatives may not capture the real level of impact for some parameters in a discrete domain, such as the number of active servers. The analysis through percentage differences, or the factorial design of experiments, fulfills such a gap.

Software aging in the eucalyptus cloud computing infrastructure: Characterization and rejuvenation

The need for high reliability, availability and performance has significantly increased in modern applications, that handle rapidly growing demands while providing uninterruptible services. Cloud computing systems fundamentally provide access to large pools of data and computational resources. Eucalyptus is a software framework largely used to implement private clouds and hybrid-style Infrastructure as a Service. It implements the Amazon Web Service (AWS) API, allowing interoperability with other AWS-based services. This article investigates the software aging effects in the Eucalyptus framework, considering workloads composed of intensive requests for remote storage attachment and virtual machine instantiations. We found problems that may be harmful to system dependability and performance, specifically regarding to RAM memory and swap space exhaustion, besides highly excessive CPU utilization by the virtual machines. We also present an approach that applies time series analysis to schedule rejuvenation, so as to reduce the downtime by predicting the proper moment to perform the rejuvenation. We experimentally evaluate our approach using an Eucalyptus test bed. The results show that our approach achieves higher availability, when compared to a threshold-triggered rejuvenation method based on continuous monitoring of resources utilization.

Experimental evaluation of software aging effects in the eucalyptus elastic block storage

The need for reliability, availability and performance has increased in modern applications, which need to handle rapidly growing demands while providing uninterrupted service. Cloud computing systems fundamentally provide access to large pools of data and computational resources. Eucalyptus is a software framework used to implement private clouds and hybrid-style Infrastructure as a Service. It implements the API Amazon Web Service (AWS), allowing interoperability with other AWS-based services. Elastic block storage is a technology which provides flexible allocation of remote storage volumes to the virtual machines running in a cloud computing environment. This work investigates the software aging effects on the Eucalyptus framework, considering workloads composed of intensive requests for attaching remote storage volumes to virtual machines. The results evidenced problems that may be harmful to system dependability and its performance due to RAM memory exhaustion and subsequent use of swap memory, besides high CPU utilization by the virtual machines and subsequent increase in the response time of applications running on the VMs.

Collagen type IV-related nephropathies in Portugal: pathogenicCOL4A3andCOL4A4mutations and clinical characterization of 25 families: Collagen type IV-related nephropathies in Portugal

Pathogenic mutations in genes COL4A3/COL4A4 are responsible for autosomal Alport syndrome (AS) and thin basement membrane nephropathy (TBMN). We used Sanger sequencing to analyze all exons and splice site regions of COL4A3/COL4A4, in 40 unrelated Portuguese probands with clinical suspicion of AS/TBMN. To assess genotype–phenotype correlations, we compared clinically relevant phenotypes/outcomes between homozygous/compound heterozygous and apparently heterozygous patients. Seventeen novel and four reportedly pathogenic COL4A3/COL4A4 mutations were identified in 62.5% (25/40) of the probands. Regardless of the mutated gene, all patients with ARAS manifested chronic renal failure (CRF) and hearing loss, whereas a minority of the apparently heterozygous patients had CRF or extrarenal symptoms. CRF was diagnosed at a significantly younger age in patients with ARAS. In our families, the occurrence of COL4A3/COL4A4 mutations was higher, while the prevalence of XLAS was lower than expected. Overall, a pathogenic COL4A3/COL4A4/COL4A5 mutation was identified in >50% of patients with fewer than three of the standard diagnostic criteria of AS. With such a population background, simultaneous next‐generation sequencing of all three genes may be recommended as the most expedite approach to diagnose collagen IV‐related glomerular basement membrane nephropathies.

Collagen type IV-related nephropathies in Portugal: pathogenic COL4A5 mutations and clinical characterization of 22 families

Alport syndrome (AS) is caused by pathogenic mutations in the genes encoding α3, α4 or α5 chains of collagen IV (COL4A3/COL4A4/COL4A5), resulting in hematuria, chronic renal failure (CRF), sensorineural hearing loss (SNHL) and ocular abnormalities. Mutations in the X‐linked COL4A5 gene have been identified in 85% of the families (XLAS). In this study, 22 of 60 probands (37%) of unrelated Portuguese families, with clinical diagnosis of AS and no evidence of autosomal inheritance, had pathogenic COL4A5 mutations detected by Sanger sequencing and/or multiplex‐ligation probe amplification, of which 12 (57%) are novel. Males had more severe and earlier renal and extrarenal complications, but microscopic hematuria was a constant finding irrespective of gender. Nonsense and splice site mutations, as well as small and large deletions, were associated with younger age of onset of SNHL in males, and with higher risk of CRF and SNHL in females. Pathogenic COL4A3 or COL4A4 mutations were subsequently identified in more than half of the families without a pathogenic mutation in COL4A5. The lower than expected prevalence of XLAS in Portuguese families warrants the use of next‐generation sequencing for simultaneous COL4A3/COL4A4/COL4A5 analysis, as first‐tier approach to the genetic diagnosis of collagen type IV‐related nephropathies.