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PCM prototype beats PCIe flash

Student boffins' box slower at large writes though

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A first-generation Phase Change Memory device has been built, faster than OCZ's VeloDrive PCIe flash card with random blockI/O but slower with sequential writes.

University of California, San Diego (UCSD) student boffins in the Computer Science and Engineering department at the Jacobs School of Engineering built their Moneta device using Phase Change Memory (PCM) chips from Micron. These use electricity to change the state of a Chalcogenide alloy from poly-crystalline to amorphous and back again.

The two states have differing resistance, read with a lesser electric current. Micron obtained the technology when it bought Numonyx. PCM technology promises to be faster than flash, but has proved difficult to productise.

The UCSD team built a Moneta emulation system in 2010, using FPGA and DRAM. It attached to its host computer system via an eight-lane PCIe 1.1 interface that provided a 2GB/sec full-duplex connection (4GB/sec total). They realised that building the PCM hardware was only one side of the coin; storage software code in device drivers and the operating system (OS) needed to change as well, and stop assuming the target storage device was slow.

In a 2010 research paper (pdf) they calculated Moneta's storage performance using the hardware emulation system:

Results for a range of IO benchmarks demonstrate that Moneta outperforms existing storage technologies by a wide margin. Moneta can sustain up to 2.2GB/sec on random 4KB accesses, compared to 250MB/sec for a state-of-the-art flash-based SSD. It can also sustain over 1.1 million 512 byte random IO operations per second [IOPS]. While Moneta is nearly 10× faster than the flash drive, software overhead beyond the IO stack (e.g., in the file system and in application) limit application level speedups: Compared to the same flash drive, Moneta speeds up applications by a harmonic mean of just 2.1×, demonstrating that further work is necessary to fully realise Moneta’s potential at the application level.

PCM prototype performance

The team has now built a Moneta system using Micron PCM chips. These are installed on Onyx cards. Judging by the hardware seen in the pictures below it is clear that the research team has had a lot of help from Micron and other identified partners; BEEcube and Xilinx, to be able to build such a sophisticated research device.

Onyx PCM card

Onyx Phase Change Memory card (UCSD)

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Next page: PCM software

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