Beyond MLC NAND: Some Perspective
There has been quite a buzz in the industry lately about NAND flash products that are capable of storing more than two bits per cell, so I wanted to just take a minute and provide our perspective.
Simply put–what ultimately matters is having the lowest cost-per-bit solution in volume production at a given moment in time, not how many bits per cell are stored. Now, that said, there’s no question that being able to store more bits per cell results in lower cost. However, there are some serious trade-offs that we think make this option not viable at this time. Most notably–performance and reliability suffer. In fact, we estimate that the performance (measured in write-cycle throughput) for going from two to three bits per cell using the same NAND architecture and process technology could be as much as halved. And reliability, (measured in write-cycle endurance) could be up to an order of magnitude worse (yes—up to 10x worse). Scary stuff. Because having a product that may have a lower bit cost, but doesn’t meet today’s level of performance and reliability limits the value of that product. It’s also worth noting the greater burden on the system implementation of going beyond today’s well-understood MLC technology, such as making sure the controller provides adequate ECC coverage.
Perhaps the most critical factor is the time frame of when the new product is introduced relative to the next-generation process technology. So, for example–most NAND manufactures introduce MLC products first on their latest-and-greatest process node, and then introduce other products as the process matures. But, if you introduce a new product with more than two bits per cell and your next-generation process technology is production-ready shortly thereafter, it is likely that your new product will not be successful, since the next generation process will provide lower cost, higher performance, and higher reliability with the good-old standard MLC.
Now, all that said, at our core we are innovators–and I’ll tell you that we are currently developing products that go beyond two bits per cell. But we also feel that the technology as a whole hasn’t come into its own just yet. It will, but what’s clear now is that lithographic scaling is the key to achieving the lowest costs while delivering the performance and reliability that the industry needs.
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2 Comments
Justin on March 10th, 2009
Hey Aidle, by dual-channeling I assume you’re referring to a RAID 0 configuration. There is absolutely a benefit to performance when using SSDs in a RAID 0 configuration. In this configuration, the load is distributed across two drives–resulting in a near doubling of the drive sub-system performance.
aidle on February 20th, 2009
Is there any overall benefits by dual-channeling two SSD together or even more?