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SSDs in the sweet spot: Modern contenders at 120-128GB


Surveying the meat of the market
— 11:01 PM on September 25, 2011

The latest generation of SSDs is out in full force. Drives are widely available from a multitude of vendors, firmware issues have for the most part been resolved, and competition has driven prices dangerously close to dollar-per-gigabyte territory. If you haven't already added a solid-state drive to your system, you should probably be thinking about it—if not salivating at the prospect.

There is certainly no shortage of lust-worthy SSDs among this crop of fresh contenders. The sheer volume of different options can be a little daunting, though. As the number of SSD vendors has grown, so has the size and complexity of their solid-state lineups. Most SSD makers have their fingers in different controller technologies and memory configurations, and don't forget the optimization-filled custom firmware that's layered on top. The end result is a landscape dotted with drives drawn from relatively shallow pools of common ingredients put together in slightly different ways.

We tried to make sense of this new wave of SSD releases as it washed up on shore earlier this year. The thing is, our initial testing was done with firmware that's now out of date and with 240-256GB drives that live outside of the average enthusiast's budget. The characteristics of those capacious drives don't always reflect the performance of the lower-capacity variants that have become affordable indulgences for enthusiasts.

Today, 120-128GB SSDs can be had for around $200, putting them right in the sweet spot typically occupied by our favorite CPUs and graphics cards. Since we don't yet have a real favorite among the current class of solid-state drives, we've spent weeks running nine SSDs through an expanded storage test suite on new Sandy Bridge hardware. Over the following pages, we'll take a closer look at Corsair's Performance 3, Force 3, and Force GT; Crucial's m4; Intel's 320 and 510 Series; Kingston's HyperX; and OCZ's Agility 3 and Vertex 3 SSDs to see which ones deserve a spot in your notebook or desktop PC.

Step up to the SSD silicon buffet
The collection of drives we've assembled for testing all hit the market this year, but the underlying controllers that act as middlemen between the NAND flash chips and Serial ATA interfaces actually span multiple years and generations. These controllers play perhaps the biggest role in dictating drive performance, so they're a good starting point.

In fact, we might as well start at the beginning, which for desktop SSDs is really Intel's original X25-M. The chip giant's first stab at a consumer-grade SSD was a remarkably consistent performer at a time when solid-state drives slowed substantially over time and were still prone to crippling bouts of stuttering. Intel designed its own 10-channel controller, and the chip remains remarkably relevant to this discussion because a very similar version of it underpins the 320 Series SSD. Yep, a controller architecture more than three years old still lives on inside Intel's newest mainstream solid-state drive.

The most obvious hint at the vintage of the 320 Series' controller silicon is its 3Gbps Serial ATA interface. That tells you a little something about this drive's chances versus competition equipped exclusively with 6Gbps SATA pipes. The 320 Series is further limited by the controller's old-school NAND interface, which tops out at 50MB/s per memory chip, and by its overly complicated name, the PC29AS21BA0.

Unfortunately, the controller's code-name, Postville Refresh, is equally uninspired. Despite retaining the original's 10 memory channels, this X25-M refresh does add a few new perks, including 128-bit AES encryption and XOR, a NAND-level redundancy scheme that works a little like a RAID 4 array. XOR guards against data loss due to irrecoverable flash failures, and it's capable of withstanding the death of an entire NAND die while keeping your Windows 7 install and carefully managed Steam folder intact.

Of the nine drives we'll be looking at today, only the 320 Series uses Intel's SSD controller. Three of the others, including Intel's own 510 Series, make use of a Marvell 88SS9174 controller whose roots can be traced back to last year's Crucial RealSSD C300. This second-generation Marvell design was the first controller to support the 6Gbps Serial ATA standard.

To keep its faster SATA interface well supplied, the 9174 supports the second-gen Open NAND Flash Interface (ONFI) specification. ONFI 2.0 allows flash chips to pass data at speeds in excess of 133MB/s, which is quite an upgrade over the gen-one spec's 50MB/s ceiling. The 9174 interfaces with those faster flash chips over eight memory channels, providing plenty of performance potential. You'll have to look elsewhere for extra features like full-disk encryption and RAID-like redundancy schemes, though.

SandForce remains the freshest face in the world of SSD controllers, and it just so happens to have the newest silicon. After storming onto the market last year with the SF-1000 series, SandForce is back with the SF-2000 family, which adds 6Gbps Serial ATA connectivity to an intriguing mix of other features. Chief among those is DuraClass, a black box of technologies that mixes compression and encryption to reduce the NAND footprint of incoming writes. Doing so not only accelerates performance, but also improves endurance by consuming fewer NAND write/erase cycles.

Although SandForce remains cagey about exactly how DuraClass' DuraWrite compression component works, we do know that it's tied to the controller's 256-bit AES encryption engine. RAISE, a NAND-level redundancy scheme similar to Intel's XOR, is also a part of the DuraClass puzzle. SandForce says RAISE functions much like a RAID 5 array, dedicating the capacity of one flash die to storing pseudo-parity data. Like XOR, RAISE is capable of surviving the failure of an entire flash die without data loss.

The SF-2281's eight memory channels are compatible with a range of flash configurations. Thus far, SandForce-based drives are largely divided into two categories: those equipped with asynchronous NAND, and those with the synchronous stuff. Synchronous NAND is the DDR of the flash world, capable of transferring data on both the rising and falling edges of a shared clock cycle. Asynchronous chips keep time with an external signal, and they're slower as a result.

Synchronous NAND can also be found in Crucial's m4. Intel declined to reveal the NAND interface for its SSDs, but I suspect the 510 Series uses synchronous chips. The Intel 510 drive is faster than the RealSSD C300, which pairs synchronous NAND with an identical Marvell controller. The Intel 320 Series is likely saddled with asynchronous flash, a side effect of its older controller tech.

Although most of the SSDs on the market draw their flash memory from asynchronous and synchronous chips based on the ONFI specification backed by Intel and Micron, a competing synchronous technology known as Toggle DDR NAND is endorsed by Toshiba and Samsung. Toggle DDR is supported by both the Marvell and SandForce controllers, but only one drive in our stack takes advantage. Corsair's Performance Series 3 has Toshiba NAND chips based on the first-generation Toggle standard, which enables per-chip transfer rates of 133MB/s, a speed that conveniently matches the starting point for the second-gen ONFI spec.

Those Toggle DDR chips are fabbed on a 34-nm process, as is the ONFI NAND lurking inside Intel's 510 Series. Otherwise, drive makers have largely made the transition to 25-nm NAND. The finer fabrication process packs more gigabytes into each silicon wafer, which is one reason why members of the latest generation of SSDs are cheaper than their forebears.