Showing posts from December, 2010

Case for RAMClouds: Scalable High-Performance Storage Entirely in DRAM

I wrote about Ousterhout's "The Role of Distributed State" work before. This review is for his recent work on RAMClouds, which appeared in SIGOPS Operating Systems Review . This paper makes a case for keeping all the data in the RAM over distributed nodes in a datacenter. "A RAMCloud is not a cache like memcached and data is not stored on an I/O device, as with flash memory: DRAM is the permanent home for data." Obviously, storing everything in RAM would yield a very high-throughput (the paper mentions 100-1000x) and very low-latency (again the paper mentions 100-1000x) system compared to disk-based systems. However, the primary reason the authors are excited about RAMCloud is the following: "RAMCloud will simplify the development of large-scale Web applications by eliminating many of the scalability issues that sap developer productivity today." The motivation for RAMCloud is to provide a general-purpose storage system that scales far beyond existing

Finding a Needle in Haystack: Facebook's Photo Storage

This paper appeared in OSDI'10. The title "Finding a needle in Haystack" is a bit over-dramatization :-) Finding a needle in Haystack becomes straightforward if you can memorize the location of each needle in the haystack. And that is exactly what Facebook Haystack system does. Haystack is an object store for sharing photos on Facebook where data is written once, read often, never modified, and rarely deleted. Haystack storage system was designed because traditional filesystems perform poorly under the Facebook workload. While using network attached storage (NAS) appliance mounted over NFS, several disk operations were necessary to read a single photo: one (or typically more) to translate the filename to an inode number, another to read the inode from disk, and a final one to read the file itself. While insignificant on a small scale, multiplied over billions of photos and petabytes of data, accessing metadata becomes the throughput bottleneck. Haystack aims to

Boxwood: Abstractions as the foundation for storage infrastructure

This paper is by Microsoft Research, and appeared in OSDI'04. This review will mostly be a stream of conciousness, because I have not yet understood all of the paper and cannot put it in context as much as I would like to. While reading in to the Boxwood paper, I started to notice how similar this is getting to the GFS problem and GFS approach . Boxwood appeared at OSDI'04, and GFS appeared at SOSP'03. Boxwood refers to GFS but does not compare or contrast itself with GFS. Maybe the reason is in 2004 the Boxwood authors could not see the similarities. This could be because, as I mentioned in my GFS review , the GFS paper did not talk about the Paxos replication of the master chunk-manager in the 2003 paper; that came a couple years later in the Chubby and Paxos-made-live papers. When citing GFS, the Boxwood authors only state that GFS "will be layered over the facilities of Boxwood". But, that is impractical as it would be duplicating a lot of the services; GFS

Globecom, WSN forum, Urban-scale sensing talk by Ed Knightly (Rice U)

Last week, I attended Globecom'10 . Ed Knightly from Rice talked about urban-scale sensing under 3 parts: vehicular sensing, health sensing, and smart grid. Ed spent most of his talk on the vehicular sensing part. A recent US deparment of transportation vehicle safety commission project asked this question: vehicles have dozens of sensors already, what if this information was shared, what can we achieve? Some low hanging fruits are: traffic signal warning, curve speed warning, left turn assistant, stop sign movement assistant, lane change warning, collision warning, and finally, internet access applications. The candidate technology that is proposed for making this networking feasible is a wireless technology, of course. But not the wifi technology which is probably many people's first guess; It is visible light communication (VLC) technology. A VLC transmitter is a LED, which can as well be the LED headlight and taillight in most of the recent models. The only thing needed is

Globecom, wireless networking forum, talk on smartphones by Roy Want

Last week, I attended Globecom'10 . Roy Want (Intel) gave a talk on smartphones in Globecom. He started by showing the market trends for cellphones smartphones and laptops. Cellphones and smartphones grow so quickly that they dwarf the laptop market (which is growing with a healthy 20%). Roy, then, asked the following question: "Will one day will we be computing on the smartphones?" He said that in order for that to happen we need to overcome the poor UI experience of smartphones. As part of these introductory slides, Roy showed a picture of the Intel atom processor for smartphones. It is smaller than rice grain yet is the brain of smartphone and x86 compatible, so these chips can bring After the presentation, over dinner, I asked Roy about why not put a dozen of these atom processors in one smartphone, given that they take virtually no space. Turns out this is currently not very feasible, because these processors are pretty battery-hungry, even though they are very ti

Onix: A Distributed Control Platform for Large-scale Production Networks

The Onix work (OSDI'10) builds on Nox. Essentially, Onix takes Nox and distributes over multiple servers. Let me start with a brief refresher on Nox. (Or you can r ead my previous post on Nox ) The main idea in Nox (and openflow) was to facilitate innovation by separating the control plane from the forwarding (data) plane. (In the current networking architecture, control and data planes are both implemented in the same place, the routers.) Nox introduced "software defined networking" (SDN): Nox uses a centralized controller to make the decisions (i.e., control plane); The routers implement only the data plane, and just follow directions from the controller while forwarding data. A drawback with Nox was that since it uses a single controller, it is prone to a single point of failure. Although the Nox work pointed out how this single controller can be distributed, it didn't pursue it further. Enter Onix. Onix investigates how to distribute that single controller. In On

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