Toshiba’s RC100 has arrived as the company’s first low-end retail NVMe SSD, and only their second retail NVMe SSD after the aging OCZ RD400. There’s nothing else quite like the RC100 in the retail SSD market, but it is part of a broader trend of PCIe and NVMe interfaces being used for cheaper SSDs, and not just the high-end drives that all the first-generation NVMe products aspired to be. Prices on these entry-level NVMe SSDs are now encroaching on the SATA SSDs that still make up the bulk of the market.
The RC100 is descended from Toshiba’s line of Ball Grid Array (BGA) SSDs for the OEM market. These drives stack the SSD controller and NAND flash memory dies in a single BGA package, making them suitable for small form factor systems that might otherwise use eMMC. Toshiba has also been mounting their BG series SSDs on M.2 2230 cards for OEMs that require upgradable storage devices. The Toshiba RC100 is based on the BG3 SSD, and the primary change in making a retail version is that the M.2 card has been lengthened to 42mm because relatively few existing systems support 30mm M.2 SSDs. This is still quite a bit shorter than the usual 80mm card length used by most consumer M.2 SSDs.
Toshiba’s first NVMe BGA SSD was the BG1 introduced in 2015. It used 15nm planar MLC NAND and a 16x20mm package with a PCIe 2 x2 interface. The next generation BG2 was the first client drive to ship with Toshiba’s 3D NAND flash memory, but it used their 48-layer design that was never competitive enough for a retail SSD. The BG3 was announced last year as part of Toshiba’s transition to their 64-layer 3D NAND that is finally good enough to fully displace their planar NAND.
The small physical size of BGA SSDs limits both the width of their host interface (to two PCIe lanes instead of the four used by high-end NVMe SSDs) and the amount of memory they have. Toshiba’s BG1 only offered 128GB and 256GB capacities, and the BG2 and BG3 only go up to 512GB. Toshiba’s BG series and the RC100 also don’t have a DRAM die in the stack, so these are DRAMless SSDs, and as we’ll see can definitely behave like one. Meanwhile thermal throttling is usually not a concern for BGA SSDs because they don’t offer the same performance as high-end NVMe SSDs, and consequently only use 2-3W under load instead of the 5-8W used by larger high-end M.2 SSDs.
To mitigate the performance limitations that result from not having a DRAM cache, Toshiba’s BG2 introduced support for the NVMe Host Memory Buffer (HMB) feature, and that has been carried over to the BG3 and RC100. HMB is an optional feature that was added in version 1.2 of the NVMe specification, released in 2014. Though the feature was standardized years ago, adoption has been slow because there hasn’t been much of a market for low-end NVMe SSDs in either the retail or OEM channels, and Microsoft’s NVMe driver didn’t implement HMB support until the Windows 10 Anniversary Update in 2016.