Samsung's 470 Series solid-state drive

Samsung makes quite a lot of different products. Their name is emblazoned on the plasma television that sits in my living room, my girlfriend's cellphone, and my sister's camcorder. The electronics giant also builds our favorite terabyte hard drive and manufactured the 17" LCDs that used to be hooked up to my primary workstation. Heck, Samsung even makes a $2,000 washing machine with something called 3D Advanced Vibration Reduction Technology. Ooooh.

You may not have any of those products, but chances are a bit of silicon made by Samsung sits inside one of the many electronic devices that are a part of your everyday life. The Korean juggernaut has a rather formidable semiconductor wing that makes everything from ARM-based processors to flash memory. With the latter, Samsung most recently had a hand in developing Toggle DDR NAND, a new kind of flash memory that promises more than triple the throughput of traditional NAND.

Although Toggle DDR NAND may eventually end up buried inside the next iDevice, the chips are coming to market first in something better equipped to take advantage of their performance potential: a 470 Series solid-state drive of Samsung's own design. Fancy flash is only one part of the equation with this new SSD, which features dual cache chips and a multi-core processor with apparent ARM underpinnings. The combination of those elements offers rather intriguing potential, so we've run Samsung's latest through our exhaustive suite of performance tests against a deep field of solid-state rivals and mechanical hard drives to see how it fares. In a moment, all the gory details.

Before diving into a mountain of benchmark data, we should take a closer look at the mix of components that make this drive tick. We used to find that an SSD's flash controller played the biggest role in determining drive performance, but I'm not sure that's still the case. As we saw with Crucial's RealSSD C300, faster flash chips can make a big difference. The RealSSD's flash conforms to the second-gen ONFI spec, which is one of two competing standards in the high-performance NAND world. ONFI counts Micron, Intel, and Hynix among its collaborators, while the competing Toggle DDR NAND standard is backed primarily by Samsung and Toshiba. Supporters of both specs have worked with the JEDEC standards body to get their offerings an official seal of approval.

Even though only Toggle DDR makes it explicit, both solutions effectively offer a double data rate by allowing reads and writes to be executed on the rising and falling edges of a data strobe. ONFI does this via a source synchronous mode that relies on the combination of a clock signal and a data strobe. In a bid to save power, Toggle DDR dispenses with the synchronous clock and gets by with a data strobe that's disabled unless transfers are actually taking place. This allows Toggle DDR to maintain an asynchronous interface and backward compatibility with controllers designed for less exotic NAND.

Source: Samsung

According to Samsung's website, the current generation of Toggle DDR NAND can enable data rates up to 133Mbps—more than a threefold increase over so-called SDR NAND, which is said to top out at around 40Mbps. I suspect those figures are for individual NAND devices rather than flash chips as a whole. Samsung's website identifies the chips used in the 470 Series as having an x8 organization that, with a max data rate of 133Mbps per device, would yield an effective 133MB/s per chip. That speed nicely matches the second-gen ONFI spec, which supports interface speeds up to 133MB/s. Subsequent ONFI revisions have added 166 and 200MB/s interface speeds, while Samsung is promising 400Mbps for a next-gen version of Toggle DDR NAND due out next year.

The 470 Series uses Samsung K8HDGD8U5M flash chips manufactured by Samsung on a 32-nano fabrication process. Moving to finer process technologies allows chip makers to squeeze more NAND dies out of a single wafer, but it also reduces the lifespan of those chips. Flash fabbed on a 50-nano process typically carries a write-erase endurance of 10,000 cycles, while 34-nano parts are generally rated for 5,000 cycles. According to Samsung, the 470 Series' flash chips have a write-erase endurance of only 3,000 cycles, which is on par with the longevity of 25-nano flash chips currently rolling off the line at Micron.

Each of the 470 Series' memory chips weighs in at 16GB, so it takes 16 of them to reach the 256GB capacity of the drive we're looking at today. Although the Toggle DDR NAND specification has a provision for low-voltage chips that require only 1.8V, these particular modules call for the same 3.3V as standard flash memory.

Along with its flash, the 470 Series sports a couple of 128MB DRAM chips. Labeled K4T1G164QE-HCE6, these puppies have a 667Mbps data rate, and Samsung puts one on each side of the drive's circuit board. SSDs typically tap a single DRAM chip as their cache memory, making this arrangement rather unusual. Add in the fact that Samsung's website makes no mention at all of the 470 Series' cache, and the intrigue builds. The dual memory chips could be treated as a single 256MB cache, but it's also possible that the drive controller uses each chip for different things. We asked Samsung for more information, but the company declined to explain exactly how the drive's caching system works.

Despite our requests for additional details, the 470 Series' S3C29MAX01 controller chip also remains a bit of a mystery. The controller is made by Samsung and is claimed to have a "multi CPU" design. However, we're still in the dark on just how many cores there are and whether their origins have something to do with the ARM initials inscribed on the chip. A dual-core design seems likely, and I very much doubt that ARM's appearance is accidential. The letters are underlined, after all.

Given the lower write-erase endurance of Samsung's Toggle DDR NAND, we were particularly concerned about the 470 Series' write amplification factor, which is calculated by dividing the amount of data written to the flash by the size of the actual write request. Unfortunately, Samsung declined to reveal specifics, leaving us to speculate once more. Drive makers want to minimize the amplification factor to preserve write-erase cycles, and without funky compression schemes like those employed by SandForce, they usually target a factor of 1. If Samsung achieved that goal, the 470 Series 256GB should be able to withstand around 750TB worth of host writes. The write amplification factor is directly related to total drive capacity, so you're looking at close to 375TB for a 128GB model, and in the neighborhood of 187TB for the 64GB variant.

Wear leveling and garbage collection algorithms are usually responsible for amplifying the amount of data written to an SSD, and the 470 Series has both. The drive also supports the TRIM command, and I suspect that the mechanism used to clear trimmed flash pages has a hand in amplifying host writes, as well.

At least we don't have to guess about the 470 Series' Serial ATA interface, which tops out at 3Gbps. The last-gen standard has since been succeeded by a 6Gbps SATA spec with higher throughput, but this SSD isn't fast enough to take advantage. According to Samsung's own performance ratings, the 470 Series tops out at 250MB/s for reads and 220MB/s for writes—speeds easily attainable within the 3Gbps spec. Those performance ratings apply to 256GB and 128GB versions of the drive, while the 64GB variant is pegged at 170MB/s for writes.

Lower-capacity SSDs tend to use fewer memory chips and thus tap fewer controller-level memory channels than their higher-capacity siblings. This leads to a reduction in performance that affects more than just sequential writes. While all three capacity points share the same 31,000 IOps rating for random reads, the 128GB model is a little behind the 256GB flagship when it comes to random writes. The 64GB drive really suffers here, offering just over half the random-write throughput of the larger drives.

Solid-state drives typically fill the 2.5" hard drive form factor to allow their memory chips to spread out on a larger circuit board. Samsung's approach is different with the 470 Series, and it hints at the company's focus on selling these drives to notebook makers. Inside the 470 Series' 2.5" casing lies an SSD whose dimensions more closely match the 1.8" hard drive form factor. You can probably expect to find variations of this drive, if not the exact circuit board, inside the next generation of ultraportable notebooks. Samsung probably has one of its own in development.

With its outer shell in place, the 470 Series doesn't look nearly as interesting. Our review sample came in a matte black casing that's considerably duller than retail samples, which have brushed aluminum enclosures with bright orange accents. It's nice to see Samsung making an effort on the aesthetics front, even if the drives will quickly be buried out of sight inside desktop or notebook systems. A little style never hurt anyone.

With Samsung's logo always highlighted in blue, orange seems like an odd choice of color. Green might have been an more appropriate hue for the 470 Series, whose idle power consumption is rated at a measly 0.14W. The drive's "active" power draw is claimed to be just 0.24W, which seems impossibly low unless Samsung's definition of active involves little more than a pulse. Toggle DDR NAND does seem to have a focus on power efficiency, though; in a moment, we'll see just how much power the 470 Series consumes in the real world.

Before getting into those and other performance results, I should point out that the 470 Series is covered by a three-year warranty. That's a pretty standard warranty length for internal hard drives, including SSDs, although some premium mechanical models do come with five years of coverage.