TORONTO — JEDEC Solid State Technology Association has approved the first standards for support of hybrid DDR4 memory modules.
The standards work is being done by JEDEC’s JC-45 Committee for Memory Modules, which developed the non-volatile DIMM (NVDIMM) taxonomy in collaboration with Storage Network Industry Association’s NVDIMM Special Interest Group (SIG), a sub-committee of SNIA’s Solid State Storage Initiative.
The new standard defines hybrid DDR4 memory modules as those that plug into standard DIMM sockets and appear like a DDR4 SDRAM to the system controller, yet contain non-volatile memories such as NAND flash on the module. These hybrid module families may share the memory channel with other standard DDR4 DIMMs. Publication of the standard is expected later this year, said Bill Gervasi, co-vice-chair of the JEDEC JC-45 Committee for DRAM Modules, in an interview EE Times.
The JEDEC standards cover two versions of hybrid modules: the NVDIMM-N, which combines DRAM and NAND flash where the flash provides backup and restore of all DRAM for reliable data persistence in the event of a power failure; and the NVDIMM-F, which provides directly addressable NAND flash that is accessed as a block oriented mass storage device.
Gervasi said these modules are supported in new DDR4 Serial Presence Detect (SPD) codes to be released later this year. In addition, new standard DDR4 DIMM labels are in the review process for release in 2015 as well, although he could not provide specific time frames. JEDEC has also defined specific signals on the DIMM connector to facilitate plug-and-play implementation of NVDIMMs on standard platforms.
When the SNIA SIG initially formed, NVDIMMs already met the mechanical dimensions defined by the JEDEC MO-269 specifications for a DDR3 DIMM module, but Gervasi said vendors were still pretty much on their own — there was a lot of infrastructure work being handled “haphazardly” by different suppliers. He said the DIMM labelling will make it easier for end users to support what they have purchased.
Viking's ArxCis-NV DDR3 NVDIMM.
For JEDEC, it’s a demonstration of how the association is now working with the entire computing architecture and not just memory modules, said Gervasi, and the JEDEC framework is flexible enough to allow for a variety of memories to be included. “NAND flash may not be the media on the other side,” he said.
Although the standards work for NVDIMM is still in its early days, there are already products available. In April, Netlist updated its NVvault product line with the introduction of its EXPRESSvault EV3 PCI Express 3.0 Non-volatile RAM, telling EE Times it was a natural extension of its NVDIMM technology, providing an alternative to flash-only options or ULLtraDIMM technology that is not dependent on the memory bus technology.
SanDisk officially started shipping its ULLtraDIMM SSD with select enterprise servers at the beginning of last year. The ULLtraDIMM SSD leverages Diablo Technologies' memory channel storage (MCS) architecture and connects NAND flash directly to the CPU through a server's memory bus; the ULLtraDIMM can be integrated into an existing DIMM slot, and additional SSDs can also be added to available DIMM slots.
Viking's ArxCis NVDIMM can be slotted into servers and RAID controllers as an alternative for battery backed-up memory modules, using supercapacitors to write to NAND flash. They can also be paired with SSDs to extend their life and performance. Meanwhile, Micron, one of the earliest participants in the SNIA NVDIMM SIG, offers NVDIMMs for use in server RAID storage, storage cache tiering, data logging, de-duplication, data logging and metadata persistent storage, as metadata must be accessed frequently and quickly in big data applications, such as data warehousing, data mining, and data analytics. The company had announced plans in early 2013 to place NAND flash along with DRAM on memory modules that ride the DDR4 bus.
SNIA created the NVDIMM SIG to foster their adoption, envisioning them as the early building blocks of computing architectures that combine storage and memory as a single entity. Launched during the 2014 SNIA Annual Members' Symposium, the NVDIMM SIG is an open community. Part of the NVDIMM SIG's mandate is to educate system vendors on incorporating NVDIMMs into their servers and platforms and to communicate industry standards to foster NVDIMM adoption and evolution in the ecosystem.
—Gary Hilson covers memory and flash technologies for EE Times and is the editor of Memory Designline.
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