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Making The Difficult Decisions

Intel SSD 510-Series 250 GB Review: Adopting 6 Gb/s SATA

Intel made a couple of interesting choices that warrant some discussion. First, it chose a controller from Marvell. And second it decided to continue using 34 nm NAND at a time when competing vendors are making the move to 25 nm.

Tapping Marvell as its controller supplier is probably most surprising. It’s not that we have any problem with Marvell. To the contrary, once Crucial’s RealSSD C300 overcame a few firmware-related growing pains, it demonstrated exceptional random read/write performance and, in part due to its 6 Gb/s interface, great sequential throughput. That was all thanks to its Marvell controller.

At the same time, I had also expected Intel to lock horns with SandForce in a more meaningful way. Given the importance of firmware and architecture to an SSD’s overall performance, I mistakenly assumed we’d be seeing a proprietary design. Intel is handling this drive series’ firmware, though. While you will see other products center on the Marvell 88SS9174-BKK2, their respective performance characteristics are sure to differ.

Intel says that it evaluated many controller options for the SSD 510 series, and the Marvell part offered the best combination of getting the drives to market, while still maintaining the quality it expected, matched to its own flash. That does not, however, mean that the next-generation 6 Gb/s drive based on 25 nm silicon will necessarily employ the same controller.

The decision to continue using 34 nm flash is telling. We know for a fact that smaller manufacturing processes affect the number of program/erase cycles that a given memory cell can withstand before it cannot be reprogrammed—a consequence of having fewer electrons holding the charge. Was Intel concerned about the long-term durability of compute-quality 25 nm NAND? That’s not likely. As you can see from the roadmap above, we’re going to see SSDs from Intel in the very near future with 25 nm NAND anyway, so that move is inevitable. Moreover, it’s in Intel’s best interest to start using 25 nm memory as soon as possible from a cost perspective.

The reasoning for 34 nm today could be related to timing. Sticking with existing technology relaxes one very important variable that could affect time to market. And the cost issue isn’t as worrisome for Intel as it might be for an SSD builder buying flash on the open market, paying spot prices. Intel has easy access to 34 nm NAND, and will continue manufacturing it through the end of this year. It can even go so far as to reserve the very best-quality dies for itself if it wants.

The choice could be related to performance, too. Endurance does drop at smaller process nodes. The speed of the memory does as well. As a result, you have to compensate in the controller, firmware, and flash, potentially slowing down development even more. Whatever the reason, on this particular product, 34 nm was the better route for Intel.

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