OpenAFS

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AFS is a distributed filesystem product, pioneered at Carnegie Mellon University and supported and developed as a product by Transarc Corporation (now IBM Pittsburgh Labs). It offers a client-server architecture for federated file sharing and replicated read-only content distribution, providing location independence, scalability, security, and transparent migration capabilities. AFS is available for a broad range of heterogeneous systems including UNIX, Linux,  MacOS X, and Microsoft Windows

IBM branched the source of the AFS product, and made a copy of the source available for community development and maintenance. They called the release OpenAFS.

via OpenAFS.

Penn Researchers Make First All-optical Nanowire Switch

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Researchers at the University of Pennsylvania have made an important advance in this frontier of photonics, fashioning the first all-optical photonic switch out of cadmium sulfide nanowires. Moreover, they combined these photonic switches into a logic gate, a fundamental component of computer chips that process information.

via Penn Researchers Make First All-optical Nanowire Switch | Penn News.

The researchers were able to measure the intensity of the light coming out of the end of the second nanowire and to show that the switch could effectively represent the binary states used in logic devices.

Which SSL certificate should I buy?

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SSL certificates that most web browsers can accept without grief are sold by a relatively small number of companies. That’s because the major web browsers are shipped with a certain set of “root certificate authorities” that they trust… and if your certificate isn’t signed by one of those authorities, or by a certificate “chained” from one of them, then you’re out of luck— the web browser will display a scary warning to the user or, in some cases, refuse to work with your site at all.

The cost of SSL certificates varies quite a bit, from as little as $20 to as much as $1,000 or more. Why such a big difference? There are three main reasons:

via WWW FAQs: Which SSL certificate should I buy?.

2. Some certificates are directly signed by a trusted root certificate, while others are “chained” from another “intermediate” certificate. This isn’t really a problem, as long as the company selling you the chained certificate really does own the root certificate. But some webmasters get confused by intermediate certificates, fail to install them correctly, and mistakenly think they have purchased a bad certificate. So chained certificates are usually less expensive to allow for this inconvenience, even though there is no real technical disadvantage.

Quantum test pricks uncertainty

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Heisenberg’s uncertainty principle, as it came to be known later, started as an assertion that when trying to measure one aspect of a particle precisely, say its position, experimenters would necessarily “blur out” the precision in its speed.

That raised the spectre of a physical world whose nature was, beyond some fundamental level, unknowable.

via BBC News – Quantum test pricks uncertainty.

Photons can be prepared in pairs which are inextricably tied to one another, in a delicate quantum state called entanglement, and the weak measurement idea is to infer information about them as they pass, before and after carrying out a formal measurement.

What the team found was that the act of measuring did not appreciably “blur out” what could be known about the pairs.

Disks from the Perspective of a File System

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Most applications do not deal with disks directly, instead storing their data in files in a file system, which protects us from those scoundrel disks. After all, a key task of the file system is to ensure that the file system can always be recovered to a consistent state after an unplanned system crash (for example, a power failure). While a good file system will be able to beat the disks into submission, the required effort can be great and the reduced performance annoying. This article examines the shortcuts that disks take and the hoops that file systems must jump through to get the desired reliability.

via Disks from the Perspective of a File System – ACM Queue.

Luckily, SATA (serial ATA) has a new definition called NCQ (Native Command Queueing) that has a bit in the write command that tells the drive if it should report completion when media has been written or when cache has been hit. If the driver correctly sets this bit, then the disk will display the correct behavior.

In the real world, many of the drives targeted to the desktop market do not implement the NCQ specification. To ensure reliability, the system must either disable the write cache on the disk or issue a cache-flush request after every metadata update, log update (for journaling file systems), or fsync system call. Both of these techniques lead to noticeable performance degradation, so they are often disabled, putting file systems at risk if the power fails. Systems for which both speed and reliability are important should not use ATA disks. Rather, they should use drives that implement Fibre Channel, SCSI, or SATA with support for NCQ.

On Linux here’s how you can check if your drive has NCQ.

$ cat /sys/block/sd?/device/queue_depth

A 1 indicates no NCQ.  and

$ cat /sys/block/sd?/device/queue_type

My green drives came back with none.

Market Leaders Drive Investment in Switching

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Terabit switch chips and switch chipsets that scale up to 400 Tbit/s are making merchant switch chips very attractive for high-performance network systems against in-house ASIC and FPGA-based designs. The latest switch devices not only deliver on performance, but integrate additional system functions such as Ethernet MACs and programmable classification engines to support software-defined networking (SDN).

via Light Reading – Market Leaders Drive Investment in Switching – Telecom.

High-performance switch devices have become both more complicated and simpler. The devices integrate additional functionality with significant on-chip memory and packet processing functions. On the other hand, the interfaces for most protocols are moving to 10 Gbit/s for the current generation and 25 Gbit/s for the next generation.

Scientists Establish First Working Quantum Network

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The team has managed to rig up a laser to fire and hit the first networked atom in a way that the atom preserves its quantum state, but also produces a photon with that information plastered onto it. The photon then shoots off down the fiber optic cable delivering it to the second atom. Network achieved. On top of that, the researchers managed to get the two networked atoms to entangle, which means the network should be completely scalable to something along the lines of an Internet.

via Scientists Establish First Working Quantum Network | Geekosystem.

NOVA series on quantum mechanics.

And another link from Cornell: Does quantum entanglement imply faster than light communication?

Say you agree to send out two beams of light to your two friends who live on opposite sides of the galaxy (you live in the middle). Ahead of time you tell them that if one of the beams of light is red the other will be blue. So you send the blue beam to your friend on one side and immediately she knows that your other friend is recieving a red beam at the same time. Aha! You say, my friends have now communicated at a speed faster than the speed of light and violated relativity, but no real information has been passed between them. You have told both of them at a normal sub-luminal speed about what you just did and that’s all. (A way of proving there’s no faster than light communication is that you could lie and send them both the same coloured beam of light and they would never know!).

Watching quantum mechanics in action: Researchers create world record laser pulse

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UCF Professor Zenghu Chang from the Department of Physics and the College of Optics and Photonics, led the effort that generated a 67-attosecond pulse of extreme ultraviolet light. The results of his research are published online under Early Posting in the journal Optics Letters.

via Watching quantum mechanics in action: Researchers create world record laser pulse.

File and Data Storage: AFS

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AFS Andrew File System is a distributed, networked file system that enables efficient file sharing between clients and servers. AFS files are accessible via the Web or through file transfer programs such as OpenAFS or Fetch Macintosh and SecureFX Windows. Currently all users with a full-service SUNet ID are granted 2 GB of AFS file space. Additional disk space is available by request for faculty-sponsored research including dissertations.

via File and Data Storage: AFS | Information Technology Services.