In March 2023, we reported that Pure Storage planned to sell 300TB SSDs within three years.
While 300TB is undoubtedly an impressive amount of storage, the company has revealed that it expects to eventually ship 1200TB SSD modules.
Shawn Rosemarin, Pure VP of R&D, explains Blocks and files that the limitations of DRAM prevent commercial off-the-shelf (COTS) SSDs from exceeding 30 TB capacity. Typically, 1 GB of DRAM is needed for every 1 TB of raw NAND capacity, meaning a 30 TB drive requires 30 GB of DRAM. The problem arises when considering larger capacities, because the amount of DRAM required matches or even exceeds that found on today’s servers.
300TB and more
Rosemarin highlighted three major issues with using more DRAM. First, DRAM fails more often than NAND. Second, DRAM is significantly more expensive. Finally, the energy efficiency of DRAM is much lower, leading to higher energy consumption.
DRAM is required for the Flash Translation Layer (FTL) software, which serves as firmware in the SSD controller. This allows incoming data to be written to different physical flash pages regardless of the intended logical block. The DRAM contains the FTL mappings and metadata for this process, making it critical to SSD operation.
However, as SSD capacities increase, the cost of DRAM becomes a larger portion of the total SSD cost.
Pure Storage’s solution to this problem is Direct Flash Modules (DFMs), which do not rely on DRAM at the disk level. Instead, the FTL is performed at a system-wide level in the Pure controller and associated software. This method, Pure claims, allows DFMs to increase capacity much faster than standard SSDs.
The company plans to release 150TB DFMs in 2025 and its roadmap states: “by the time the industry starts shipping 25-30TB HDDs and 30-60TB SSDs at scale in 2026, we expect to ship 300TB DFMs. ”
That’s just the beginning. Although he didn’t even give a timetable for it, Rosemarin said Blocks & Files, “We plan to scale beyond 300, to 600 and even to 1.2 petabytes per DFM.”
Of course it won’t be cheap. Last year, the company said the price per gigabyte of its 300TB drive would be “less than” $0.15/GB. If we do some simple calculations, and don’t take into account inflation and everything else that can happen before it even hits the market, a 1.2 PB bracket would be well over $180,000.