Flash-optimized storage is rapidly becoming the new standard for most enterprise and mid-size corporate IT departments. Meanwhile, the underlying chip technology, called NAND flash, continues to rapidly evolve, driven by demand for higher capacities, better performance and increased reliability.
In particular, while traditional two-dimensional (2D) or planar NAND has made significant improvements over the years in capacity and cost, it has scaled about as far as it can go. That’s why Nimble Storage has already supplemented our product line with high-capacity three-dimensional (3D) NAND TLC solid-state drives (SSDs).
At Nimble Storage, we’ve dedicated a lot of engineering cycles to leveraging dense packaging to improve scalability and performance. For instance, we were among the first to add NVDIMMs (Non-Volatile Dual In-line Memory Modules) to our arrays a couple of years ago. Indeed, Nimble’s strategy and its CASL file system have always focused on delivering the right balance of performance and capacity in the most efficient way.
What is driving the shift to 3D NAND?
Flash chip manufacturers are always looking to shrink their fabrication process and allow for more transistors to be stored on the same die. This increases chip density at almost no extra cost, but there are some significant ramifications. As the die shrinks, fewer electrons are trapped in the cells and the cells themselves become more susceptible to electron leakage. This can lead to cells not been able to hold a charge, or to provide false readings.
This problem becomes even more pronounced if a cell has to store multiple charges, known as multi-level cell or triple level cell (MLC/TLC NAND). As a result, most semiconductor manufacturers have said they are not going to pursue further scaling of 2D or planar NAND beyond the current 15nm diameter, and instead will shift their engineering and manufacturing resources to 3D NAND MLC/TLC.
What is 3D NAND?
3D NAND overcomes the density limitations of 2D NAND by stacking chips vertically, thereby enabling manufacturers to get more bits per chip than they could just by lithography shrinking. That also translates to lower cost per gigabyte ($/GB). That’s why 3D NAND is a disruptive technology – one manufacturer has said its 40nm 3D NAND is able to produce an equivalent lithography of a 10nm 2D NAND, which means mass production provides great scalability at a low cost.
Unlike 2D NAND, 3D NAND uses a Charge Trap (CTF) instead of a Floating Gate. A Charge Trap requires lower programming than a Floating Gate, consumes less power, and is more resistant to wear. That means there is less risk of cell-to-cell interference, resulting in better bit error rates than a Floating Gate. Additionally, because the cell diameter is larger, endurance is increased. That’s why 3D NAND is inherently more reliable than 2D planar NAND.
For all these reasons, we expect 3D NAND flash chips to increase in popularity, and will leverage them in Nimble’s industry-leading data architecture to provide our customers with maximum performance, endurance, and cost-efficiency.