PCIe接口才是固态硬盘以后大势所趋

有一群厂商打算推出采用 PCI Express (PCIe)总线的固态硬盘(SSD)，号称可改善目前采用 Serial ATA (SATA)或是Serial-Attached SCSI (SAS)接口的固态硬盘性能；新一波产品将延续SATA与SAS两种协议分庭抗礼的局面，并让市场竞争重点加速转向新软件功能。 去年，包括戴尔(Dell)、英特尔(Intel)、美光(Micron)、甲骨文(Oracle)与Stec等共80家厂商，组织了一个产业团体着手定义 NVMe (Non-Volatile Memory Express)接口标准，采用该标准的首批固态硬盘预计在今年稍晚上市。 在此同时，另一个产业组织SCSI Trade Association (STA)最近宣布，将采用ANSI T10技术委员会所订定的、以PCI Express标准为基础的SCSI接口(SCSI Express)。STA将于5月初在美国硅谷举行技术研讨会，届时该组织成员应该会展示首款支持SCSI Express接口的固态硬盘。 分属不同阵营的NVMe 与SCSI Express 固态硬盘，预期将延续目前SATA与SAS两种指令集在闪存储存碟与硬盘机领域的竞争态势；而以上两种固态硬盘对新创公司 Fusion-io 来说则是一项挑战，该公司是因率先让固态硬盘搭载快速的PCIe总线、与系统中央处理器紧密连结而声名大噪。 大多数第一代的固态硬盘还是采用速度较慢的SATA或SAS接口，这两种接口在服务器的互连接口中层级较低。PCIe的性能优势让Fusion-io最近一季的销售业绩达到8,400万美元，其表现让该公司在过去两年成功募集了超过3亿美元的资金。 随着越来越多的PCIe固态硬盘将在今年上市，Fusion-io所面临的是双重挑战：其一，当标准化硬盘产品的供应量增加，将加速该类产品的价格下滑；其二，更多固态硬盘的出现，可能会削弱该公司采用独家技术达成的产品性能优势。 Fusion- io研发了一种方法，能让主CPU快速存取固态硬盘内的内存；该公司的专利技术号称能将固态硬盘内资料存取位置的“地图”提供给主CPU，让写入存取的延迟时间低于15微秒(microseconds)。大多数的硬盘产品仍较少着墨控制器上的logical-to-physical转译地图功能，因此有较高的延迟。 新的NVMe 与 SCSI Express标准能让供货商利用共通的PCIe固态硬盘软件堆栈，可降低其成本并缩短产品上市时程。“目前大多数的PCIe固态硬盘都有自己专属的驱动软件，缺乏产业标准软件；”NVMe组织发言人、英特尔资深储存工程师Amber Huffman表示，利用NVMe的一致性功能集：“我们可望达成更快的产品上市时程与更高的渗透率。” 在Fusion- io这厢，其产品部门副总裁Gary Orenstein表示，该公司将支持SCSI Express阵营，因为他们是遵循经业界共同认可的标准团体──ANSI T10技术委员会的工作；而采用NVMe规格则需要签署一份由该阵营带头者英特尔主导的授权文件。“NVMe 与 SCSI Express标准的兴起将带来的影响还有待观察；有人认为这两种标准终有一天会融合。”他补充指出。 到目前为止，Fusion-io最近三季的业绩主要来自三大服务器厂商客户的贡献，包括戴尔、惠普(HP)与IBM；其中戴尔已经透露其最新服务器产品将支持NVMe标准，为Fusion-io前景带来些许阴霾。 本文下一页：竞争重点转向软件 本文授权编译自EE Times，版权所有，谢绝转载

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{pagination} 还有一种新趋势是，可带来附加价值的软件逐渐成为固态硬盘守住价格底线的秘密武器；对此Fusion-io表示，软件现在是该公司研发工作的主要关键；Fusion-io并在去年8月砸下6,500万美元收购了一家储存虚拟化(storage virtualization)软件供货商IO Turbine。 Fusion- io已经推出了重新命名的ioTurbine软件，能让执行VMWare虚拟化软件的服务器，把固态硬盘当高速缓存用；该公司还预见了能让固态硬盘进军 其它应用领域的软件商机，那些领域包括数据库、企业搜寻软件(enterprise search)以及社交游戏(social gaming)。 以这种模式，Fusion-io可望藉由各种支持快闪记忆碟的应用程序软件，再次引领固态硬盘市场风潮；不过长期看来，固态硬盘产业还需要更多的标准化工作以及来自各种操作系统的支持，让闪存储存更能融入系统内存阶层。 对各方来说，好消息是目前固态硬盘产业还在起步阶段，仍有取得高成长率的潜力；根据市场研究机构IDC的预估，PCIe接口固态硬盘市场在2010年至 2015年间将取得85%的平均复合年成长率(CAGR)；就连速度较慢的SATA与SAS接口固态硬盘，在预测期间的CAGR也可达到56%。PCIe 固态硬盘在2009年还名不见经传，但在2011年出货量已达2~3亿颗。 NVMe组织的Huffman认为，长远来看，PCIe接口产品将会取代SATA、甚至SAS产品；她指出，SATA接口的进展在目前的6 Gbps版本后就停滞，下一步是与PCIe的融合：”SAS接口会在超越12Gbps时遇到瓶颈，我们未来必然会看到PCIe成为终极方案。” Huffman 表示，产业界对NVMe的兴趣浓厚，而且工程师们迄今已经为该规格添加了约20个勘误表；目前已经有授权产品正在开发阶段：”我们举办了不少说明会，这意味着人们确实在采用该规格。”NVMe在新罕布什尔大学(University of New Hampshire)设置了一个互通性测试实验室，该实验室并进行该接口的扩展，包括支持多主机以及省电功能的选项。 编译：Judith Cheng 本文授权编译自EE Times，版权所有，谢绝转载 参考英文原文：Solid-state drives jump on PCI Express，by Rick Merritt

相关阅读：
• 西部数据亮相IDF 2012：谁说超极本一定要用SSD？
• 固态存储新时代，Nand Flash当家做主站起来
• 笔记本厂商进军Ultrabook将面临的几大问题ZP7esmc

{pagination} Solid-state drives jump on PCI Express Rick Merritt SAN JOSE, Calif. – A wide group of vendors is poised to roll solid-state drives for the PCI Express bus, promising improved performance over current flash drives that mainly use serial ATA and Serial-Attached SCSI interfaces. The wave of new products will continue the current split between SATA- and SCSI-based protocols, and accelerate the shift to competition based on new software features. As many as 80 companies including Dell, Intel, Micron, Oracle and Stec are part of the trade group that defined the NVMe interface last year. The first drives using the interface are expected to ship later this year. Separately, the SCSI Trade Association (STA) recently announced it will adopt the SCSI over PCI Express standard being completed by the ANSI T10 committee. STA will hold a technology showcase in Silicon Valley on May 9 where members may demo some of the first SCSI Express flash drives. The competing NVMe and SCSI Express drives are expected to continue the same split between SATA and SCSI command sets that exists in today’s SATA and SAS flash and hard-disk drives. The NVMe and SCSI Express drives represent a challenge to Fusion-IO, a startup that soared to success based on pioneering the move to plugging solid-state drives into the fast PCIe bus, closely linked to system CPUs. Most first-generation solid-state drives used the slower SATA and SAS hard drive interfaces that reside lower in the hierarchy of interconnects on a server. The performance benefits of PCIe helped Fusion IO tap into sales that soared to $84 million in its most recent quarter. The strong sales supported two successful public offerings in the past two years, raising more than $300 million. With the advent of many more PCIe flash drives this year, Fusion faces a two-fold challenge. A wider supply of standard drives could help speed price decreases in the sector. In addition, the presence of more solid-state drives will likely narrow Fusion’s performance benefits based on its proprietary approach. Fusion pioneered a method of giving host CPUs fast access memory stored on flash drives. The company has a proprietary approach for sharing with the host processors a map that describes where all the data on a flash drive physically resides, enabling write access at latencies of as little as 15 microseconds. Most drives maintain less comprehensive logical-to-physical translation maps on the drive controllers and thus have higher latencies. The new NVMe and SCSI Express specs will enable vendors to leverage common software stacks for PCIe drives, lowering their costs and time-to-market. “Today most PCIe flash drives include a proprietary driver and no industry software standard,” said Amber Huffman, a spokeswoman for the NVMe group and a senior principal storage engineer at Intel. With NVMe’s consistent feature set, “we expect to see faster time-to-market and broader adoption,” she said. For its part, Fusion will back the SCSI Express approach because it is based on the work of a recognized standards group, the ANSI T10 committee. Access to the NVMe spec requires signing a legal document managed by Intel Corp., the group’s leader, said Gary Orenstein, vice president of products at Fusion IO. “Is too early to tell what the shift to NVMe and SCSI Express will mean,” said Orenstein. “Some people think there could be a merging of the two efforts eventually,” he added. To date, nearly three-quarters of Fusion’s sales have gone to three large customers, likely the top server makers—Dell, Hewlett-Packard and IBM. Dell has already signaled its support for NVMe in its latest servers, casting a shadow over at least one of Fusion’s big customers. Shift to software Value-added software is increasingly the secret sauce for maintaining flash drive prices. For its part, Fusion says software is now the key focus of its R&D efforts, and it acquired IO Turbine, a developer of storage virtualization software, in August for $65 million. Fusion is already shipping the renamed ioTurbine software. It enables solid-state drives to be used as memory caches on a server running VMWare virtualization software. Fusion sees opportunities to roll software that enables other applications with its flash drives in areas such as database, enterprise search and social gaming. In this way, Fusion may again be pioneering the direction for the rest of the flash drive market—a move to flash-enabled applications software. Long term, the industry still needs broader standards and support from operating systems for how flash storage can fit into the memory hierarchy. The good news for all sides is it’s still early days for solid-state drives with plenty of growth seen ahead. International Data Corp. expects the market for PCIe-based flash drives to expand 85 percent on a compound basis from 2010-2015. Even the older market for slower SATA and SAS flash drives will grow a solid 56 percent over that period, IDC predicts. PCIe-based flash drives came from virtually nowhere in 2009 to sales of 200 to 300 million units in 2011, according to various market researchers. Long term, PCIe will supplant SATA and perhaps SAS as well, said Huffman. SATA development ended at the current 6 Gbit/second generation with a SATA/Express merger planned as the next step. “SAS will have trouble getting beyond 12 Gbit/s—we definitely see PCI Express as the future,” Huffman said. Interest in the NVMe spec is strong based on engineers adding about 20 errata to the spec to date, a sign products are in development. “We’re processing lots of clarifications, and that means people are using the spec,” she said. The group has interoperability test labs set up at the University of New Hampshire and it is working on extensions to the spec. They include options for supporting multiple hosts and power-saving features.