OTTAWA, Canada – PCI Express (PCie) has proven itself to be superior to technologies such as SATA and SAS, but does it have an expiry date?
Diablo Technologies is offering one alternative to traditional PCIe implementations through its Memory Channel Architecture. Jerome McFarland, the company’s principal product marketer, said PCIe has a great deal of theoretical bandwidth, but in reality it has inherent limitations because it is not a native storage interface -- it requires an onboard controller to manage resources between the flash memory and server I/O.
McFarland said handling such large amounts of flash creates complexity that ultimately limits performance and reliability of the controller, so despite having access to a wide pipe, PCIe-based SSDs aren’t able to really take advantage of the bandwidth. As outstanding I/O requests scale beyond controller thresholds, he said, latency increases dramatically.
Diablo’s memory channel architecture addresses these PCIe limitations by connecting NAND flash directly to the CPU through a server’s memory bus. Persistent memory is attached to the host processors of a server or storage array. This configuration allows for linear scalability in performance at extremely low latencies. The company has already seen some adoption of the technology for financial services applications that require high performance, and forged a partnership with SanDisk on ULLtraDIMM technology for servers.
In Gartner’s recent “Cool Vendors in In-Memory Computing, 2014” report, Michele Reitz, Gartner senior research analyst for semiconductors, writes “as a result of sitting directly on the faster memory channel, the SSDs can achieve drastically lower latencies than any existing solid-state storage solution, and can function as a less expensive and nonvolatile alternative to DRAM memory, if the slower access speeds are acceptable for the application.”
By email, Reitz told me Diablo’s technology has much potential, and that in some cases, the SanDisk/Diablo collaborative technology could replace the need for PCIe. But it’s important to note it is installed in the memory slots, and operates quite differently than storage and requires changes in the BIOS and OS for the host server.
In addition, Reitz said products using Diablo’s technology are very new to market, will take time to penetrate, and customers will need to be educated on their benefits. The storage market moves fairly slowly in the acceptance of new technologies in the mainstream, noting a slower adoption of PCIe overall than expected, so the uptick in solid-state NVDIMM technologies for storage will take some time.
Meanwhile, PCIe still has its advantages, said Reitz, particularly its scalability. If you start with one lane and add another, you double the bandwidth, up to 32 lanes on a single card, because it is a direct high-speed serial connection, not a bus with a bottleneck. This means that when multiple devices want to transmit data, they are not sharing the same data path to the CPU. Reitz said that as PCIe moves from 1.0 to 2.0 and 3.0 to 4.0, the result will be clock speed increases and thus the throughput should increase as well.
There is a roadmap for PCIe for the next five years, noted Reitz. Products with gen 3.x will be available roughly from now until 2017, with gen 4 coming in the 2018 timeframe. Generally the Intel platform transitions provide a guide for the adoption of new standards, she said, so the transition to Grantley and subsequent processor releases will shed light on the next transition for PCIe.
Eric Burgener, research director for IDC’s storage practice, agrees Diablo’s approach is ideal for some uses cases. From a storage perspective, PCIe made sense for applications that do not require a lot of availability or capacity, and provides a storage option that sits right inside a server. “It completely negated the network hop and latencies associated with go to some sort of SAN device.”
In an enterprise environment, Burgener said, where high availability and redundancy is expected, a SAN device ensures data is replicated in more than one place. This has not yet been addressed in the PCIe world, he said. “But there’s tons of applications that can benefit from faster storage in smaller capacities and it’s much cheaper.”
Companies such as Diablo are focusing on applications that don’t require redundancy but do require very high performance, said Burgener. “So there’s a market specific for this. It’s a great fit and much lower in cost compared to any SAN environment.”