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New flash memory technologies promise faster, denser storage

Flash is front and center as Western Digital launches 96-layer 3D NAND enterprise SSDs, and Toshiba unveils new SSD form factor and ultrafast XL-Flash chips.

Storage admins have a number of new flash memory technologies to check out this week, including dense 96-layer 3D NAND storage drives, ultrafast XL-Flash chips and a new small form factor for high-performance NVMe-based memory devices.

Toshiba Memory America developed the thin 14-mm-by-18 mm-by-1.4-mm XFMExpress form factor – which is between the size of a camera's SDHC card and a cell phone's microSD card -- for notebook PCs, gaming consoles and automotive, surveillance and Internet of Things (IoT) devices.

XFMExpress is a removable storage technology designed to enable users to easily replace or upgrade a device. It supports NVMe 1.3 and PCI Express (PCIe) 3.0 to enable up to 4 GB per second of bandwidth over four lanes, and future releases will support up to 8 GBps with PCIe 4.0, according to Toshiba. Although XFMExpress is on display at this year's Flash Memory Summit, Toshiba is only demonstrating it at this point and still working on a standardization plan, so the technology won't be broadly available any time soon.

A more imminent flash memory option that Toshiba plans to begin sampling next month is single-level cell (SLC) XL-Flash chips that fill the performance gap between conventional NAND flash and more expensive DRAM, as well as Intel's Optane 3D XPoint technology. Toshiba unveiled low-latency XL-Flash at the 2018 Flash Memory Summit, a year after Samsung discussed its similar SLC-based Z-NAND technology, and said it expects mass production in 2020.

Western Digital SSD
Western Digital Ultrastar DC SN640 SSD form factor options

Broad availability should come sooner for 96-layer triple-level cell (TLC) 3D NAND solid-state drives (SSDs) from multiple suppliers. Western Digital got started with its first data-center NVMe-based SSDs to use the denser flash memory technology. The Ultrastar DC SN640 and SN340 models will sample this quarter and ship in higher volume in the fourth quarter, according to Eddie Ramirez, a senior director of product marketing for Western Digital's data center devices.

The 96-layer 3D NAND technology should help to drive down costs for enterprise SSD customers, according to Jim Handy, general director and semiconductor analyst at Objective Analysis.

The cost will come down because the more layers you have, the lower the cost per gigabyte, and the amount of flash storage will take up less space on the datacenter floor and consume less power in general.
Jim HandyGeneral director and semiconductor analyst, Objective Analysis

"The cost will come down because the more layers you have, the lower the cost per gigabyte, and the amount of flash storage will take up less space on the datacenter floor and consume less power in general," Handy said.

Western Digital previously shipped an Ultrastar DC SN630 model with 64-layer 3D NAND in the most popular 2.5-inch U.2 form factor used in storage systems and servers. With the 96-layer refresh, the company will support two additional form factors: a long, ruler-like Enterprise and Data Center Small Form Factor, or E1.L, at a maximum capacity of 30.72 TB, and a 22-mm-by-110-mm, gumstick-shaped M.2 SSD storing up to 3.84 TB.

The Ultrastar DC SN640 brings support for up to 128 NVMe namespaces to enable customers to subdivide a single drive and provide designated storage space for individual virtual machines or application workloads, Ramirez said.

The SN640 supports mixed read-write workloads such as SQL Server, MySQL and hyper-converged infrastructure. The 2.5-inch U2 model offers two endurance options: 0.8 drive writes per day (DWPD), at a capacity range of 960 GB to 7.68 TB, and 2.0 DWPD, with storage from 800 GB to 6.4 TB. The M.2 and E1.L SSDs support 0.8 DWPD.

"We're seeing a general trend that, as capacities get higher in these drives, you don't need as many drive writes per day," Ramirez said. "It's not just in NVMe. We're seeing it in SAS as well. Users at one point were using 10 drive writes. Then they became comfortable with three drive writes, then one, and now we're starting to get into that sub-one category as well."

Western Digital's new Ultrastar SN340 is designed strictly for "very read-intensive" workloads, at 0.3 DWPD, with capacities of 3.84 TB and 7.68 TB in the 2.5-inch U.2 form factor. The SN340 targets applications that write in large block sizes, including content delivery networks, video caching and NoSQL databases with about 90% reads and 10% writes, Ramirez said.

Demand uncertain for XFMExpress, XL-Flash

The level of demand for Toshiba's new-fangled XFMExpress form factor and XL-Flash chips is unclear at this point. The success of XFMExpress could depend on whether Toshiba and its partners get the technology into a standards committee, such as the Storage Networking Industry Association (SNIA) or Joint Electronic Device Engineering Council, said Greg Wong, founder and principal analyst at Forward Insights.

Toshiba flash
Toshiba plans to start sampling ultrafast XL-Flash technology in September 2019.

Widespread industry support from OEM customers will be another key hurdle for Toshiba with XFMExpress, according to Joseph Unsworth, a research vice president at Gartner.

"To gain massive adoption, it will require many PC OEMs and other mobile device makers to drive the scale necessary to make this cost competitive. I just don't see this happening in the next few years," Unsworth said.

Toshiba partnered with Japan Aviation Electronics on the hardware design and Lenovo on the Flash Memory Summit demonstration. The company plans to open up its XFMExpress technology to the broader market and pursue industry standardization, according to Grant Van Patten, a product line manager in the company's SSD business unit.

"Any new form factor is going to take a while for adoption, so we don't necessarily expect this to catch fire overnight. We obviously have to work on the outreach and the standardization portion so that momentum will carry this into more devices in the future," Van Patten said. "Obviously that's going to require a lot of work from our side, but we think it's worth it because of the pain points we're solving."

Toshiba's XL-Flash technology

Toshiba's XL-Flash aims to give enterprises a less expensive, ultra-low latency alternative to DRAM and Intel's Optane technology. The company claims XL-Flash's 128 GB SLC die enables high reliability, its 16-plane architecture reduces latency, and the 4KB page size facilitates more efficient reads and writes. XL-Flash's read latency could be as low as 5 microseconds, and the performance could be 10 times faster than existing TLC NAND, according to Toshiba.

Initial XL-Flash deployments will be in the SSD form factor, according to Scott Nelson, senior vice president and general manager of Toshiba's memory business unit. But Nelson said he can envision future XL-Flash use in non-volatile dual in-line memory modules in the storage class memory layer.

Industry analysts predict the market for XL-Flash could be limited to niche use cases. Gartner's Unsworth said XL-Flash could serve as a more reliable, higher performance cache or tier to lower quality flash options, such as TLC or quadruple-level cell (QLC) NAND. But Unsworth cautioned that XL-Flash would come at a significant price premium to TLC and QLC flash.

Handy said the SLC chip market is small and production is low, so the price is about 20 times the cost of TLC NAND flash and close to DRAM. "This will narrow the market for XL-Flash," Handy said.

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