Ensuring solid-state drives are up to scratch: Data buffering scheme improves performance of solid-state drives

A data buffering scheme improves the performance of solid-state drives in large-scale, data-intensive applications.

Solid-state drives (SSDs) store digital information using electronic circuits. The power efficiency of SSDs and their ability to read and write data quickly means that they are becoming the primary storage device in computers. A major drawback of SSDs, however, is the limited number of times that data can be stored and deleted -- an aspect that hinders the use of these devices for data-intensive applications known as data-center environments.

Qingsong Wei and co-workers at the A*STAR Data Storage Institute and National University of Singapore have developed a scheme for writing data to SSDs that could circumvent these problems to make solid-state drives useful for an even broader range of applications.

SSDs divide their storage space into distinct areas called blocks. A computer can either save large files across consecutive blocks -- a process known as sequential writing -- or write smaller files in blocks scattered throughout the device -- so-called random writing.

The researchers conducted an intensive workload study of the distribution of read and write request sizes over ten real enterprise workload traces supplied by the Storage Network Industry Association. They found that the highest traffic was from small, random requests of less than 64 kilobytes in size.

Generally, random writing is much slower -- by as much as four times -- than sequential writing. One way around this bottleneck is to use part of the memory as a 'buffer'. The buffer briefly stores data as it comes into the drive, which then enables sequential writing at a later time. Current buffer management approaches improve sequential writing but only at low buffer usage, wasting expensive buffer space.

Wei's team helped to solve this problem through an alternative approach that categorizes the data in the buffer by its popularity, which reflects how frequently the data is likely to be needed. The scheme retains popular blocks in the buffer, rather than deleting them, and sequentially writes less popular blocks to the SSD.

"Our buffer management scheme can increase sequential writing with high buffer utilization, thus improving performance and extending the lifetime of the SSD," says Wei.

The researchers tested the approach and demonstrated that the so-called popularity-aware buffer management scheme, or PAB, can achieve an improvement in performance of up to 72 per cent and triple the device lifetime compared to existing schemes. "Our method reduces the cost of SSDs by improving buffer utilization and is easy to implement," explains Wei. "Our next step will be to design smarter SSDs by integrating these same ideas with emerging non-volatile memory."

Journal Reference:

Qingsong Wei, Lingfang Zeng, Jianxi Chen, Cheng Chen. A Popularity-Aware Buffer Management to Improve Buffer Hit Ratio and Write Sequentiality for Solid-State Drive. IEEE Transactions on Magnetics, 2013; 49 (6): 2786 DOI: 10.1109/TMAG.2013.2249579

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Quantum physics secures new cryptography scheme

The way we secure digital transactions could soon change. An international team has demonstrated a form of quantum cryptography that can protect people doing business with others they may not know or trust -- a situation encountered often on the internet and in everyday life, for example at a bank's ATM.

"Having quantum cryptography to hand is a realistic prospect, I think. I expect that quantum technologies will gradually become integrated with existing devices such as smartphones, allowing us to do things like identify ourselves securely or generate encryption keys," says Stephanie Wehner, a Principal Investigator at the Centre for Quantum Technologies (CQT) at the National University of Singapore, and co-author on the paper.

In cryptography, the problem of providing a secure way for two mutually distrustful parties to interact is known as 'two-party secure computation'. The new work, published in Nature Communications, describes the implementation using quantum technology of an important building block for such schemes.

CQT theorists Wehner and Nelly Ng teamed up with researchers at the Institute for Quantum Computing (IQC) at the University of Waterloo, Canada, for the demonstration.

"Research partnerships such as this one between IQC and CQT are critical in moving the field forward," says Raymond Laflamme, Executive Director at the Institute for Quantum Computing. "The infrastructure that we've built here at IQC is enabling exciting progress on quantum technologies."

"CQT and IQC are two of the world's largest, leading research centres in quantum technologies. Great things can happen when we combine our powers," says Artur Ekert, Director of CQT.

The experiments performed at IQC deployed quantum-entangled photons in such a way that one party, dubbed Alice, could share information with a second party, dubbed Bob, while meeting stringent restrictions. Specifically, Alice has two sets of information. Bob requests access to one or the other, and Alice must be able to send it to him without knowing which set he's asked for. Bob must also learn nothing about the unrequested set. This is a protocol known as 1-2 random oblivious transfer (ROT).

ROT is a starting point for more complicated schemes that have applications, for example, in secure identification. "Oblivious transfer is a basic building block that you can stack together, like lego, to make something more fantastic," says Wehner.

Today, taking money out of an ATM requires that you put in a card and type in your PIN. You trust the bank's machine with your personal data. But what if you don't trust the machine? You might instead type your PIN into your trusted phone, then let your phone do secure quantum identification with the ATM (see artist's impression). Ultimately, the aim is to implement a scheme that can check if your account number and PIN matches the bank's records without either you or the bank having to disclose the login details to each other.

Unlike protocols for ROT that use only classical physics, the security of the quantum protocol cannot be broken by computational power. Even if the attacker had a quantum computer, the protocol would remain secure.

Its security depends only on Alice and Bob not being able to store much quantum information for long. This is reasonable physical assumption, given today's best quantum memories are able to store information for minutes at most. Moreover, any improvements in memory can be matched by changes in the protocol: a bigger storage device simply means more signals have to be sent in order to achieve security. (The idea of 'noisy storage' securing quantum cryptography was developed by Wehner in earlier papers.)

To start the ROT protocol, Alice creates pairs of entangled photons. She measures one of each pair and sends the other to Bob to measure. Bob chooses which photons he wants to learn about, dividing his data accordingly without revealing his picks to Alice. Both then wait for a length of time chosen such that any attempt to store quantum information about the photons is likely to fail. To complete the oblivious transfer, Alice then tells Bob which measurements she made, and they both process their data in set ways that ensure the result is correct and secure within a pre-agreed margin of error.

In the demonstration performed at IQC, Alice and Bob achieved a random oblivious transfer of 1,366 bits. The whole process took about three minutes.

The experiment adapted devices built to do a more standard form of quantum cryptography known as quantum key distribution (QKD), a scheme that generates random numbers for scrambling communication. Devices for QKD are already commercially available, and miniaturised versions of this experiment are in principle possible using integrated optics. In the future, people might carry hand-held quantum devices that can perform this kind of feat.

"We did the experiment with big and bulky optics taking metres of space, but you can well imagine this technology being shrunk down to sit happily next to classical processing circuits on a small little microchip. The field of integrated quantum optics has been progressing in leaps and bounds, and most of the key pieces required to implement ROT have already been successfully demonstrated in integrated setups a few millimetres in size," says Chris Erven, who performed the experiments at IQC as a PhD student under the supervision of Raymond Laflamme and Gregor Weihs. Weihs is now at the University of Innsbruck, Austria. Erven is now a postdoctoral fellow at the University of Bristol, UK.

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