RAMCloud is a storage system that provides low-latency access to large-scale datasets. To achieve low latency, RAMCloud stores all data in DRAM at all times. To support large capacities (1PB or more), it aggregates the memories of thousands of servers into a single coherent key-value store. RAMCloud ensures the durability of DRAM-based data by keeping backup copies on secondary storage. It uses a uniform logstructured mechanism to manage both DRAM and secondary storage, which results in high performance and efficient memory usage. RAMCloud uses a polling-based approach to communication, bypassing the kernel to communicate directly with NICs; with this approach, client applications can read small objects from any RAMCloud storage server in less than 5μs, durable writes of small objects take about 13.5μs. RAMCloud does not keep multiple copies of data online; instead, it provides high availability by recovering from crashes very quickly (1 to 2 seconds). RAMCloud's crash recovery mechanism harnesses the resources of the entire cluster working concurrently so that recovery performance scales with cluster size. 7:2 J. Ousterhout et al.[Ritchie and Thompson 1974]. Over the past 15 years, the use of DRAM in storage systems has accelerated, driven by the needs of large-scale Web applications. These applications manipulate very large datasets with an intensity that cannot be satisfied by disk and flash alone. As a result, applications are keeping more and more of their long-term data in DRAM. By 2005, all of the major Web search engines kept their search indexes entirely in DRAM, and large-scale caching systems such as memcached [Memcached 2011] have become widely used for applications such as Facebook, Twitter, Wikipedia, and YouTube.Although DRAM's role is increasing, it is still difficult for application developers to capture the full performance potential of DRAM-based storage. In many cases, DRAM is used as a cache for some other storage system, such as a database; this approach forces developers to manage consistency between the cache and the backing store, and its performance is limited by cache misses and backing store overheads. In other cases, DRAM is managed in an application-specific fashion, which provides high performance but at a high complexity cost for developers. A few recent systems such as Redis [2014] and Cassandra [2014] have begun to provide general-purpose facilities for accessing data in DRAM, but their performance does not approach the full potential of DRAMbased storage.This article describes RAMCloud, a general-purpose distributed storage system that keeps all data in DRAM at all times. RAMCloud combines three overall attributes: low latency, large scale, and durability. When used with state-of-the-art networking, RAM-Cloud offers exceptionally low latency for remote access. In our 80-node development cluster with QDR Infiniband, a client can read any 100-byte object in less than 5μs, and durable writes take about 13.5μs. In a large datacenter with 100,000 nodes, we expect small reads to compl...

We compared the gut microbial populations in 100 women, from rural Ghana and urban US [50% lean (BMI < 25 kg/m2) and 50% obese (BMI ≥ 30 kg/m2)] to examine the ecological co-occurrence network topology of the gut microbiota as well as the relationship of short chain fatty acids (SCFAs) with obesity. Ghanaians consumed significantly more dietary fiber, had greater microbial alpha-diversity, different beta-diversity, and had a greater concentration of total fecal SCFAs (p-value < 0.002). Lean Ghanaians had significantly greater network density, connectivity and stability than either obese Ghanaians, or lean and obese US participants (false discovery rate (FDR) corrected p-value ≤ 0.01). Bacteroides uniformis was significantly more abundant in lean women, irrespective of country (FDR corrected p < 0.001), while lean Ghanaians had a significantly greater proportion of Ruminococcus callidus, Prevotella copri, and Escherichia coli, and smaller proportions of Lachnospiraceae, Bacteroides and Parabacteroides. Lean Ghanaians had a significantly greater abundance of predicted microbial genes that catalyzed the production of butyric acid via the fermentation of pyruvate or branched amino-acids, while obese Ghanaians and US women (irrespective of BMI) had a significantly greater abundance of predicted microbial genes that encoded for enzymes associated with the fermentation of amino-acids such as alanine, aspartate, lysine and glutamate. Similar to lean Ghanaian women, mice humanized with stool from the lean Ghanaian participant had a significantly lower abundance of family Lachnospiraceae and genus Bacteroides and Parabacteroides, and were resistant to obesity following 6-weeks of high fat feeding (p-value < 0.01). Obesity-resistant mice also showed increased intestinal transcriptional expression of the free fatty acid (Ffa) receptor Ffa2, in spite of similar fecal SCFAs concentrations. We demonstrate that the association between obesity resistance and increased predicted ecological connectivity and stability of the lean Ghanaian microbiota, as well as increased local SCFA receptor level, provides evidence of the importance of robust gut ecologic network in obesity.

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These data suggest that infused CD34+ cell count is predictive of kinetics of lymphocyte recovery after ASCT and is an independent prognostic factor for OS and EFS after ASCT in patients with NHL.