UCSD非易失性存储工作室——耐久性主存的铺路人
还记得上一篇博文中我提到过一个特别的咒语——大家不要再把NVM当作快速存储设备，而要将它看成是（慢速）存储设备！看起来，我并不是唯一持有这个想法的人，在由UCSD的两个研究小组组织的NVM工作室的讨论中，处处体现出了这一假设的精神。
，另一张则陈列了PMC在开展的 提供了更多关于Donard的信息。会上有许多精彩的主题演讲、技术论坛及展板展示等等。在此，我想分享一些我认为引人注目的亮点。请注意：我并未能聆听到所有的讨论，所以这只是个人参与活动的一些观感：
§ 主题演讲：今年共有三场主题演讲。Samsung的Bob Brennan和Seagate的Phil Brace的演讲均比较高层，焦点放在HG-NVM出现后将会带来的存储增长与变化。Intel 的Andy Rudoff则采取不同的视角，演讲更加技术性，广受听众赞赏。其演讲深入阐述了Intel的ISA和Linux是如何改变以适应持久性主存。三个演讲的内容均十分丰富详实。
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§ 内存设备：内存公司一直在讲要推出NV-NVM。然而，实际数据还是不太明确，而今市场上只有Everspin量产了DDR3 ST-MRAM产品（目前密度尚低）。NAND从2D向3D的过渡确实让 NAND扩展生机复燃，其他替代技术眼下看起来也不再象此前那么有吸引力。我们仍然继续梦想着有一种持久性的内存技术，从访问时间、成本及耐久度等指标来看，性能介乎DRAM与NAND之间。
§ SSD技术的发展：我目前感兴趣的一个领域是基于主机的FTL SSD。此类设备将眼下放在SSD上的“智能”（如垃圾回收）移至主机之上。确然无疑地，此类设备的大规模部署即是实证，显示着NAND上的成本支出能由此得到大幅度缩减。百度在此提供了一篇相关的优秀论文。由哥本哈根信息科技大学（IT University of Copenhagen）PhilipeBonnet领导的一个研究小组也在此领域开展了有效的工作，并通过OpenChannelSSD项目提供了开源代码。另外一个话题是“数据感知型SSD”,关注点在于如何使用（从应用层提供的）提示信息来告知（感知型）SSD在何处及如何存放数据，以使性能及耐久度达到最高。
§ 应用：应用需要如何改变以支持NVM，这个领域受到了广泛的关注。单单改变操作系统是不够的。比如，近来已经看到Hadoop 及其NoSQL通过诸如Aerospike 改进了对NVM的支持。前Fusion-IO（而今的SanDisk）在会上作了一场有关如何利用NVM来改善SQL压缩性能的精彩演讲。
总而言之，今年的NVM工作组成绩卓著。研究NVM技术的团队人才济济，大家为NVM进行的操作系统及应用层面的优化日益增多。我相信，，随后的12个月内，还将会取得非常多重要的进展，无疑将为下一届NVM工作室的成功打下坚实的基础！
UCSD Non-Volatile Memory Workshop – Paving the Way for PersistentMain-Memory
Recall from my last blog that I have a mantra – Let’s stop thinking aboutNVM as fast storage and start thinking about it as (slow) memory! Well it seemsI am not alone in that thinking, as this premise was very well represented atthe NVM Workshop organized by two of the research groups at UCSD.
PMC had the pleasure of being aPlatinum Sponsor at this year’s event and I always consider this to be thetechnical counter-point to Flash Memory Summit. The event is a lot smaller thanFMS but more technically orientated with a nice mix of industrial and academicspeakers. I have been attending for three years now and always find it a greatplace to catch up on people’s research and meet graduate students (who might bepersuaded tocome work for PMC).
This year a record 212 peopleregistered with 52% being industrial, 45% academic and 3% other (i.e.government). PMC had two posters at the event. One of these looked atcontrolling QoS metrics in NVMeSSDs, the other looked at some recent developments inour open-source Donard project. You canread more about Donardhere. There were some great keynotes, technicalsessions and posters and I wanted to call out some of my highlights. Pleasenote: I did not make it to all the talks, so this is just my view of whatI saw at the event:
§ Keynotes: Thisyear we had three keynotes. Both Bob Brennan (Samsung) and Phil Brace (Seagate)were a bit more high level with a focus on storage growth and changes that willoccur as HG-NVM come on board. Andy Rudoff (Intel),took a different tack andwent technical, which I think this audience appreciated, delving into howIntel’s ISA and Linux are changing to accommodate persistent main memory. Allthree talks were very informative but Andy’s definitely won the Geek award ;-).
§ ErrorCorrection: The workshop always has a strong ECC component.This year we saw a continued discussion on Write Once Memory (WOM) codes. WhileI like WOM codes from a theory point of view, I struggle to see how they can beused in practical SSDs given that they sacrifice capacity for endurance, andtherefore increase that golden metric of $/GB. However, I am quite happy to beproven wrong. We also saw some improvements to LDPC codes (a topic very close to my heart), for NVM. I did not see much onECC for NG-NVM, which is a shame as I think the low latencies predicted forthose memory types will place new pressures on ECCs, and this an area I wouldlike to see more research in.
见过旅行风景，就这样，慢慢学会了长大。
