Last week the Storage Networking Industry Association (SNIA) hosted its 2012 Storage Developer Conference (SDC). There was a strong focus on SSDs at this forum, with 15 papers, one keynote, and a panel devoted to the subject.
Consider that the 2008 SDC was the first such conference in which SSDs were discussed. This year I commented to another participant: “Some day we will look back on this transition and be amazed at how suddenly SSDs became fundamental to the way storage is configured!”
Many of those papers and keynotes made it clear that the PCI Express (PCIe) interface has become the one to watch. Although only four of the presentations used “PCIe” in their titles, at least half thoroughly covered PCIe, and the panel was dedicated to the PCIe interface. There are several other well-accepted SSD interfaces: SATA, SAS, and even Fibre Channel. Why this focus on PCIe?
Existing HDD interfaces have been highly optimized to get the most out of a spinning disk. Since an SSD has no spinning disk, its communication with the world has to be reconfigured in order to make it agree with these HDD interfaces, and this reduces its speed and performance. In an ideal world the NAND flash would communicate with the host processor through a memory interface.
Although PCIe isn’t a memory interface, it does provide a lot of bandwidth, so it can more closely couple the processor with NAND flash. As The SSD Guy understands, PCIe was designed with graphics co-processors in mind, as a way to allow the graphics chip to be very speedily controlled by the processor.
Furthermore, by abandoning standard HDD interfaces, the software can bypass slower elements of the I/O stack that help bring the processor’s I/O request into conformance with the SAS, SATA, and Fibre Channel protocols.
Things are not as simple as they might appear, though. Today there aren’t the tight standards covering PCIe-based storage that already exist for SATA, SAS, and Fibre Channel. This was the subject of a number of the SDC presentations – how do we get PCIe to the same level of standardization as already exists for those other protocols? The industry is fortunate that solid standards organizations have already started working on initiatives to solve this problem.
Why is this so important? Let’s put it this way: If there were no standards a user might not be sure that the PCIe SSD bought from one company would actually work in another company’s server. At best the problem would be immediately clear, and another SSD or server would be purchased to replace the faulty one. True, some money would be wasted on the components that didn’t match up, but not all that much. At worst some obscure problem would appear after the system had been in use for a number of months, and costly downtime would result until the cause of the problem was determined and a correction implemented.
In a nutshell, expect SSDs to proliferate in the data center over the next few years, with PCIe SSDs becoming the interface of choice. SSDs won’t replace HDDs, but will find their way into nearly all systems as a means of accelerating access to data stored in HDDs.
Readers may be interested to know that Objective Analysis has published a report covering high-end SSDs: The Enterprise SSD – Technologies & Markets that can be purchased for immediate download from our website.