NVMe-oF Delivering While Persistent Memory Remains Mostly Promise

This article, published on March 28, 2019, was written by Ken Clipperton, lead analyst for storage, DCIG LLC.

NVMe-oF Delivering While Persistent Memory Remains Mostly Promise

The Persistent Memory Summit held in late January 2019 provided a good view into the current state of industry. Some key technologies and standards related to persistent memory are moving forward more slowly than expected. Others are finally transitioning from promise to products. This article summarizes a few key takeaways from the event as they relate to enterprise storage systems.

Optane is Gap Filler in Storage Hierarchy, Not DRAM Replacement
One fact made clear across multiple presentations is that Optane (Intel’s brand name for 3D XPoint phase-change memory) fills an important gap in the storage hierarchy, but falls short as a non-volatile replacement for DRAM. Optane has excellent read latency and bandwidth, so its deployment as a persistent read-cache as HPE is doing may be its primary use case in enterprise storage systems.

MRAM is Ready, But Waits on DDR5 and NVDIMM-P Standards
The main surprise for me from the event was the extent to which MRAM has become a real product. In addition to Everspin and Avalanche, both Intel and Samsung have announced that they are ready to ship STT-MRAM (spin-transfer torque magnetic RAM) in commercial production volumes.

The initial focus of MRAM shipments is embedded devices, where the necessary surrounding standards are already in place and where the capacity, endurance and low power requirements of MRAM make it a great fit with the requirements of next-generation embedded edge devices.

One factor holding back MRAM and other storage-class memories from being used in standard servers and enterprise storage systems is the lack of critical standards. The NVDIMM-P standard for placing non-volatile memory on DDR DIMMs was originally expected to be completed in 2018, as was the DDR5 standard. Neither JEDEC standard has been completed, and no firm date for their release was provided.

Persistent Storage Moving Onto NIC
One development that surprised me was the move to place MRAM on network interface cards. The idea is to persist writes on the NIC before the data leaves the host server, eliminating the network from the write-latency equation. It will be interesting to see how providers implement this capability.

NVDIMM-N Remains Predominant Non-Volatile DRAM Technology for 2019 and 2020
The predominant technology for providing non-volatile memory on the memory buss is based on NVDIMM-N standard. These NVDIMMs pair DRAM with flash memory and a battery or capacitor. The DRAM handles I/O until a shutdown or power loss triggers the contents of DRAM to be copied to the flash memory. Thus the module provides the performance of DRAM and the persistence of flash memory.

NVMe-oF Delivers in 2019 and 2020
If the DDR5 and NVDIMM-P standards are published by the end of 2019, we may see MRAM and other storage class memory technologies make their way into enterprise storage systems by 2021.

In the meantime, enterprise storage providers will focus on integrating NVMe and NVMe-oF into their products to provide advances in storage performance. Multiple vendors are already shipping NVMe-oF compliant products. These include E8 Storage, Pavilion Data Systems, Kaminario, and Pure Storage.