The reliability measures in today's disk drive-based storage systems focus predominantly on protecting against complete disk failures. Previous disk reliability studies have analyzed empirical data in an attempt to better understand and predict disk failure rates. Yet, very little is known about the incidence of latent sector errors i.e., errors that go undetected until the corresponding disk sectors are accessed.Our study analyzes data collected from production storage systems over 32 months across 1.53 million disks (both nearline and enterprise class). We analyze factors that impact latent sector errors, observe trends, and explore their implications on the design of reliability mechanisms in storage systems. To the best of our knowledge, this is the first study of such large scale -our sample size is at least an order of magnitude larger than previously published studies -and the first one to focus specifically on latent sector errors and their implications on the design and reliability of storage systems.
With use of standardized techniques, a study of nasopharyngeal pneumococcal carriage in children in six Central and Eastern European cities was undertaken during the winter of 1993-1994. Nasopharyngeal swab specimens were collected from 954 children (predominantly under the age of 5 years) who were hospitalized or attending outpatient clinics or day-care centers. Susceptibility of isolates was determined by disk diffusion (on Mueller-Hinton agar with 5% sheep blood). Disks containing 1 micrograms of oxacillin were used to screen for susceptibility to penicillin G. Pneumococci were recovered from 258 (27.0%) of the 954 children. A variety of strains were recovered, and most penicillin-resistant strains were ŕesistant to multiple agents. Minimum inhibitory concentrations of penicillin for selected resistant strains were 0.125-8 micrograms/mL. Resistance to penicillin was common in strains from Bulgaria, Romania, and Slovakia. Resistance to erythromycin and chloramphenicol occurred in Bulgarian and Romanian strains. Strains from Poland were all susceptible to penicillin, but many were resistant to tetracycline. Resistance to trimethoprim-sulfamethoxazole was common in Bulgarian, Romanian, and Slovak strains. Czech and Russian strains were predominantly susceptible to antibiotics. Most resistant strains were of serotypes 6, 14, 19, and 23.
Recent work describing six named species and two unnamed genomospecies within Citrobacter has enlarged the genus to 11 species. DNA relatedness and phenotypic tests were used to determine how well these species can be identified. One hundred thirty-six strains were identified to species level by DNA relatedness and then identified phenotypically in a blinded fashion. By using conventional tests, 119 of the 136 strains (88%) were correctly identified to species level. Three additional strains (2%) were identified as citrobacteria but were not identified to species level, and 14 strains (10%) were misidentified as other Citrobacter species. Carbon source utilization tests were used to identify 86 of the strains. Eighty-four strains (98%) were correctly identified, and two strains (2%) were misidentified as other Citrobacterspecies. Additional strains of Citrobacter genomospecies 10 and Citrobacter genomospecies 11 were identified, allowing these species to be formally named as Citrobacter gilleniisp. nov. and Citrobacter murliniae sp. nov., respectively.
Abstract. The load balancing framework for high-performance clustered storage systems presented in this paper provides a general method for reconfiguring a system facing dynamic workload changes. It simultaneously balances load and minimizes the cost of reconfiguration. It can be used for automatic reconfiguration or to present an administrator with a range of (near) optimal reconfiguration options, allowing a tradeoff between load distribution and reconfiguration cost. The framework supports a wide range of measures for load imbalance and reconfiguration cost, as well as several optimization techniques. The effectiveness of this framework is demonstrated by balancing the workload on a NetApp Data ONTAP GX system, a commercial scale-out clustered NFS server implementation. The evaluation scenario considers consolidating two real world systems, with hundreds of users each: a six-node clustered storage system supporting engineering workloads and a legacy system supporting three email severs.
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