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Transcend Information has
announced a new type of SuperMLC (multi-level cell) NAND that it
believes can satisfy the needs of enterprise customers who prize both
speed and reliability, while offering the lower price points and mass
manufacturing advantages that characterize conventional MLC memory.
Modern NAND flash can hold one, two, or three bits of information per cell. Single-bit NAND is called SLC (single-level cell), two-bit NAND is MLC, and three-bit NAND is TLC (triple-level cell). While the exact specifications and reliability ratings for each type of flash vary from company to company, SLC NAND is the fastest and most durable, followed by MLC, followed by TLC.
The graph below shows how this plays out in terms of programming voltage for MLC vs. SLC NAND.
Note that when writing, the voltage to write each cell has to be precisely calibrated for MLC, whereas SLC can happily swing across the 1V – 3V range. I couldn’t find an equivalent graph for TLC, but imagine eight distinct voltage squeezed into the same space as MLC’s four curves, and you’ve got the idea. It takes longer to program TLC cells, and the cells themselves degrade much more quickly.
As for endurance, the graph below shows how TLC, MLC, and SLC stack up. The EM-MLC line is for a specific company’s product, and isn’t necessarily relevant to this discussion without knowing a great deal more about what Transcend is implementing.
SLC NAND is very fast, very durable, and extremely expensive, MLC NAND is the middle-of-the-road consumer option, and TLC still offers significant performance improvements compared to conventional HDDs, but is unsuitable for heavy professional use or enterprise deployments.
Over the last 24 months, a number of companies have introduced hybrid drive management schemes to leverage the capabilities of SLC and the cost-effectiveness of either MLC or TLC. Samsung’s 840 EVO and 850 EVO drives use a slice of each TLC NAND chip as SLC, greatly improving performance. Crucial and several other companies also dynamically allocate part of their drive as SLC, adjusting this cache as required depending on how full the drive is.
What Transcend is doing is binning high-quality MLC, then treating it like SLC. In theory, this provides 4x the write performance and up to 30,000 program/erase cycles. That’s not identical to what the graph above illustrates, but it’s close enough for our purposes — specialized MLC-as-SLC can offer better performance and endurance than standard MLC, but at lower costs. Combine this approach with the additional reliability and performance we’ve seen from 3D NAND ,and manufacturers may soon be able to offer MLC-as-SLC products with capabilities that fully rival conventional 2D planar SLC.
For now, Transcend is confining this capability to its industrial hardware. But if the concept proves sound, we’re almost guaranteed to see it deployed in a high-end consumer drive. NAND flash technologies tend to debut in enterprise or industrial settings first, so the fact that Transcend isn’t jumping to push this tech into consumer hardware doesn’t mean we won’t see that happen within a year.
Modern NAND flash can hold one, two, or three bits of information per cell. Single-bit NAND is called SLC (single-level cell), two-bit NAND is MLC, and three-bit NAND is TLC (triple-level cell). While the exact specifications and reliability ratings for each type of flash vary from company to company, SLC NAND is the fastest and most durable, followed by MLC, followed by TLC.
The graph below shows how this plays out in terms of programming voltage for MLC vs. SLC NAND.
Note that when writing, the voltage to write each cell has to be precisely calibrated for MLC, whereas SLC can happily swing across the 1V – 3V range. I couldn’t find an equivalent graph for TLC, but imagine eight distinct voltage squeezed into the same space as MLC’s four curves, and you’ve got the idea. It takes longer to program TLC cells, and the cells themselves degrade much more quickly.
As for endurance, the graph below shows how TLC, MLC, and SLC stack up. The EM-MLC line is for a specific company’s product, and isn’t necessarily relevant to this discussion without knowing a great deal more about what Transcend is implementing.
SLC NAND is very fast, very durable, and extremely expensive, MLC NAND is the middle-of-the-road consumer option, and TLC still offers significant performance improvements compared to conventional HDDs, but is unsuitable for heavy professional use or enterprise deployments.
Over the last 24 months, a number of companies have introduced hybrid drive management schemes to leverage the capabilities of SLC and the cost-effectiveness of either MLC or TLC. Samsung’s 840 EVO and 850 EVO drives use a slice of each TLC NAND chip as SLC, greatly improving performance. Crucial and several other companies also dynamically allocate part of their drive as SLC, adjusting this cache as required depending on how full the drive is.
What Transcend is doing is binning high-quality MLC, then treating it like SLC. In theory, this provides 4x the write performance and up to 30,000 program/erase cycles. That’s not identical to what the graph above illustrates, but it’s close enough for our purposes — specialized MLC-as-SLC can offer better performance and endurance than standard MLC, but at lower costs. Combine this approach with the additional reliability and performance we’ve seen from 3D NAND ,and manufacturers may soon be able to offer MLC-as-SLC products with capabilities that fully rival conventional 2D planar SLC.
For now, Transcend is confining this capability to its industrial hardware. But if the concept proves sound, we’re almost guaranteed to see it deployed in a high-end consumer drive. NAND flash technologies tend to debut in enterprise or industrial settings first, so the fact that Transcend isn’t jumping to push this tech into consumer hardware doesn’t mean we won’t see that happen within a year.
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