NVMe is a popular interface due to its increasing use in the client and enterprise space, so the perception that it is used only in hefty datacenter-class SSDs is gone. However, some are still surprised to find it used in mobile devices, such as phones, tablets and 2-in-1s.
Toshiba announced that it would have a live demo of its new BG series of products at the Flash Memory Summit 2016 next week. These new NVMe SSDs come in the smallest of form factors, such as small M.2 2230 (22x30mm) and BGA (Ball Grid Array) packages.
Toshiba introduced its first NVMe BGA package last year, and Marvell also introduced its own Alta Plus NVMe controller for embedded applications. Apple has used NVMe in many of its devices, including its phones, for some time, so the specification has traction in mobile use cases.
In the meantime, others are also migrating to the UFS specification, which allows for both embedded and removable cards, such as Samsung's latest UFS cards and phones. UFS and NVMe both have the ability to process read and write operations simultaneously (serial interface), which makes them more attractive than the parallel eMMC interface that appears to be fading into low-end mobile devices.
Toshiba/WD recently announced that its BiCS 3D NAND would come to market shortly. The new BG series NVMe SSDs come packing the highly-anticipated BiCS NAND, but Toshiba is being coy and not revealing if it's BiCS 2 or 3, though we do know that it is of the TLC variety, which increases density and reduces cost.
Toshiba touts the PCIe 3.0 x2 solution as 90 percent smaller than a normal 2.5" SSD and 82 percent smaller than a standard M.2 2280 SSD. The BGA package weighs only a gram (or less), but it still manages to cram in 126, 256 or 512 GB of capacity. Toshiba uses its own homegrown controllers, which allow it to infuse custom features that help increase performance and reduce power consumption (2.8W active/5mW idle).
“We are thrilled to unveil the new BG series with BiCS FLASH, which will deliver both a rich feature set and high performance all within an extremely small footprint and power profile,” said Jeremy Werner, vice president of SSD marketing and product planning, at Toshiba America Electronic Components, Inc. “We expect to be in production this year with BiCS FLASH BGA SSDs, offering our customers a compelling and cost-effective storage solution for the next generation of high performance ultra-thin and light notebooks and tablets.”
The new Toshiba BG SSDs employ the HMB (Host Memory Buffer) NVMe functionality, which we covered in depth earlier this year. In short, HMB allows a DRAM-less SSD to utilize a portion of the system memory to cache its LBA lookup tables, which boosts performance and reduces overall power consumption and cost. HMB is promising, and we expect to see the tactic used widely in the future, but it requires BIOS and driver optimizations. Currently, there is no support in mainstream devices, so it is far from plug-and-play. Toshiba is working to assist OEMs in developing products that utilize the HMB functionality.
You can still use the SSD without HMB, but it will reduce performance significantly, which effectively eliminates the gains listed above. However, Toshiba did not reveal any hard performance data yet, but we will be sure to visit the demo at the Flash Memory Summit and update accordingly.
Toshiba's implementation uses only 32 MiB of host memory to manage a 16 GiB LBA range, which the company feels is enough to speed performance for most users. The BG SSDs also have only a small portion of the SSD LBA tables cached, which will have performance implications in case of cache "misses."
Some SSDs with limited DRAM also employ a similar tactic of caching only hot spots, but these tend to fall in the low-cost segment. The requirement for 32 MiB of DRAM to manage 16 GiB of NAND is interesting because most SSDs require 1 MB of DRAM for every 1 GB of NAND, and the Toshiba implementation is using twice as much. Toshiba mentioned that the driver is still in the optimization phase, but it will be interesting to see if other HMB solutions also require extra DRAM for table lookups.
The drives support TCG/Pyrite and TCG/Opal encryption, which is an important differentiator. Toshiba is currently sampling its BGA SSDs to a limited number of PC OEMs, but it will expand availability in 4Q 2016.