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Intel's 520 Series solid-state drive


A new muse for Intel's 25-nm NAND
— 10:00 AM on February 6, 2012

Intel has gotten a lot of mileage out of the SSD controller it designed for the original X25-M. This chip made its debut in 2008, back when Justin Bieber was underground. Since then, the same controller architecture has been stretched over three generations of consumer drives. With each refresh have come firmware enhancements and new flash memory chips built using finer fabrication techniques. The latest in that lineage is the Intel 320 Series, which features 25-nm MLC NAND.

Despite this cutting-edge flash, the 320 Series can't keep up with the performance of its contemporary rivals. That doesn't seem to bother Intel, whose long-term relationship with the controller has become an open one. Last year, Intel hooked up with a Marvell controller for the high-end 510 Series SSD. Although the 6Gbps controller had already been used by Crucial in the C300, Intel brought its own flash and firmware to the party, plus faster performance.

The Intel 510 Series uses older 34-nm NAND, so it's long overdue for a transition to cheaper, faster, 25-nm flash. Rather than sticking with the Marvell controller, Intel dumped it for a new muse: SandForce's SF-2281, which you'll recognize from SSDs like the OCZ Vertex 3, Corsair Force Series GT, Kingston HyperX, and a stack of others. The SandForce controller has been widely praised for its performance, but much of its early life was tarnished by a pesky BSOD bug.

Intel took its time with the controller, which is why Cherryville, otherwise known as the 520 Series SSD, is hitting the market long after rival drive makers released similar offerings. With only the finest Intel NAND and exclusive firmware improvements, this latest entry into the high-end SSD market promises better performance than existing SandForce implementations and solid reliability that Intel is backing up with a five-year warranty. Is this the SandForce SSD you've been waiting for? Let's take a closer look to find out.

Scuffed outside, SandForce inside
On the surface, the Intel 520 series looks all but identical to the 320 Series. The case dates back to the second-generation X25-M, and there's good reason for Intel to keep using it. See that black metal rim framing the face of the case? It's a spacer that brings the drive up to the 9.5-mm thickness common among 2.5" SSDs, mechanical hard drives, and notebooks. Without the spacer, the metal case measures only 7 mm thick, allowing it to slip into slimmer systems.

The utilitarian design isn't particularly flashy, but the brushed metal top piece has a nice finish. Unfortunately, the same can't be said for the bottom of the case, which looks like it's been kicked across the pavement and run over with a belt sander.

The scuffs are much clearer in person, and they can't be buffed out. This isn't just a one-off thing, either; similar scuff patterns can be found on all the Intel SSDs we have with this case design.

Intel says the case meets its "form, fit and function" requirements, of course. For an SSD line that scales up to a 480GB model that sells for $999, aesthetics should probably be a part of that equation. Kingston and Samsung have put together particularly attractive cases for their SSDs, and I'm a sucker for the Ferrari-red paint that covers Corsair's Force Series GT. Intel would do well to follow those leads or, at the very least, to clean up the design it already has. The distressed look may work for trendy furniture and designer denim, but it's a poor fit for high-tech products.

But I digress. The real action occurs inside the case, which is where we find SandForce's SF-2281 controller. Intel has long insisted it continues to develop its own proprietary controller technology, but there's no telling when the firm will have a next-gen design ready for public consumption. Until then, Intel seems content to respin its existing controller for low-end drives and use third-party solutions to service the high end of the consumer market.

Intel maintains that the X25-M's controller was designed in-house only because the alternatives available at the time weren't up to snuff. The Marvell 88SS9174 proved itself robust enough to anchor the Intel 510 Series SSDs, and now the SandForce SF-2281 has been deemed worthy of powering its replacement, the 520 Series.

As far as controllers go, the SF-2281 is about as exotic as they come. We took a closer look at its architecture in our early peek at the OCZ Vertex 3, so I won't recount all of the nerdy details here. The chip has, after all, been making the rounds for about a year now. It does have a few characteristics worth highlighting, though. Like the Marvell chip behind the Intel 510 Series, the SandForce controller sports eight memory channels and a 6Gbps Serial ATA interface. All the usual memory types are supported by the chip, whose internal buffers are large enough that a separate DRAM cache isn't required.

Pulling off a cacheless design is a neat trick, but it's not nearly as intriguing as SandForce's DuraClass technology, which includes everything from write compression to RAID-like redundancy. DuraClass has persisted through two generations of SandForce controllers, and its inner workings remain a closely guarded secret. One component is DuraWrite, a lossless, on-the-fly compression scheme used to reduce the size of incoming writes from the host. Writing less data to the flash should speed write performance provided the data is sufficiently compressible. Reducing the NAND footprint of incoming writes can also increase the lifespan of the flash, which is bound by a limited number of write-erase cycles. The less data is written to the flash, the fewer write-erase cycles are consumed.

Should individual flash cells or even an entire die burn out, the Intel 520 Series will be protected by RAISE, a RAID-like technology that falls under the DuraClass umbrella. Short for Redundant Array of Independent Silicon Elements, RAISE behaves similar to a RAID 5 array by spreading data and parity bits across multiple NAND dies. Like RAID 5, you have to give up storage capacity in exchange for redundancy. RAISE consumes the capacity of one flash die, which is why SandForce-based SSDs come in capacities like 60, 120, and 240GB rather than 64, 128, and 256GB.

In addition to RAISE, the SandForce controller features an ECC error-correction engine. Another engine handles 256-bit AES encryption. Because this encryption can't be turned off, we suspect it's an integral part of the whole DuraClass bit-scrambling process. By default, SandForce-based SSDs are configured with blank passwords to ensure users have unfettered access to their data.