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SSD scaling outside the sweet spot

A look at performance scaling from 120-320GB

Ever since I started reviewing PC components here at TR, my relationship with hardware has become increasingly promiscuous. The Ikea shelving unit that serves as my test rack plays host to an endless stream of new systems—at least one every week, and when I'm really on my game, several in one day. I'm not incapable of commitment, though. The Twins, our tireless tandem of storage test systems, are firmly entrenched on my rack. Since being updated with Sandy Bridge hardware and an expanded test suite late this summer, this tag team has been running almost non-stop benchmarking the latest solid-state drives.

We broke in the duo with a massive round-up of 120-128GB SSDs. With prices in the $200 range, these drives occupy the sweet spot in the market. They're not the fastest examples of the breed, though. Manufacturer spec sheets routinely promise better performance for higher-capacity models. Modern SSDs situate their flash arrays behind multi-channel memory controllers, so adding NAND dies can allow drives to take advantage of more controller-level parallelism.

How much of a performance boost can you really get from a higher-capacity SSD? I'm glad you asked. For the past few weeks, The Twins have been chewing through a collection of 240-320GB versions of the same drives from our 120-128GB round-up. The numbers have been crunched, graphs have been drawn, and value has been quantified. So, without further ado, let's introduce the subjects of today's look at SSD performance scaling.

One of everything
The SSD market is made up of a dizzying number of different drives, but it's important to realize the number of unique configurations is considerably smaller. Three factors influence performance: the SSD controller, the flash memory, and the firmware that manages the interactions between those things and the host interface. Only a handful of controllers and flash memory types are actively being used by top-tier drive makers. Firmware is typically supplied by the folks behind the controller, and there isn't always room to extract additional performance via additional tweaking.

In our sweet-spot SSD round-up, we tested similar SandForce drives from three manufacturers. Despite each one having a slightly different firmware revision, the drives offered essentially equivalent performance across the entirety of our benchmark suite. We did see substantial performance gaps between SandForce configurations using synchronous and asynchronous memory, so that's where we've focused our attention today. Corsair's Force Series 3 will represent budget drives based on the SandForce SF-2281 controller and equipped with asynchronous NAND, while Corsair's Force Series GT speaks for more exotic models populated with synchronous flash.

  Size Controller NAND Cache Warranty Price
Corsair Force Series 3 120GB SandForce SF-2281 25-nm Micron NA 3 years $180
Corsair Force Series 3 240GB SandForce SF-2281 25-nm Micron NA 3 years $330
Corsair Force Series GT 120GB SandForce SF-2281 25-nm Intel NA 3 years $204
Corsair Force Series GT 240GB SandForce SF-2281 25-nm Intel NA 3 years $460
Crucial m4 128GB Marvell 88SS9174 25-nm Micron 128MB 3 years $198
Crucial m4 256GB Marvell 88SS9174 25-nm Micron 128MB 3 years $381
Intel 320 Series 120GB Intel PC29AS21BA0 25-nm Intel 64MB 5 years $205
Intel 320 Series 300GB Intel PC29AS21BA0 25-nm Intel 64MB 5 years $545
Intel 510 Series 120GB Marvell 88SS9174 34-nm Intel 128MB 3 years $280
Intel 510 Series 250GB Marvell 88SS9174 34-nm Intel 128MB 3 years $569

Among contemporary SSDs based on Marvell's 88SS9174 controller, Intel's 510 Series and Crucial's m4 are the most recent examples. The m4 is decked out with 25-nm synchronous flash chips similar to the ones found inside the Force GT, while the 510 Series uses older 34-nm NAND. Intel and Crucial have their own firmware, as well, so we've included examples of both drives.

The latest controllers from SandForce and Marvell are easily the most popular with SSD makers right now. Intel's 320 Series provides a unique alternative that pairs an old-school 3Gbps controller of Intel's own design with 25-nm NAND that rolls out of the company's fabs. Since this example of vertical integration is part of Intel's push to get SSDs into mainstream machines, we couldn't leave it out of the fun.

From a parallelism perspective, the 320 Series' flash controller has somewhat of an edge over its 6Gbps competition. The Intel chip has 10 memory channels, while the Marvell and SandForce designs must make do with only eight. The individual memory channels on the Intel controller are slower than the ones on its rivals, though.

Drive makers differ on whether they offer 120 or 128GB capacities in the sweet spot. There's even more variety at higher capacity points. The SandForce crowd doubles up on its 120GB variants with 240GB versions. Crucial multiplies by two, as well, scaling its 128GB m4 up to a 256GB version. Intel's 510 Series starts at 120GB but makes its next stop at 250GB, providing a little more capacity than the SandForce drives. While the 320 Series also offers a 120GB capacity, it leaves 250GB in the dust on the way to 300GB.

Storage capacity is perhaps better discussed in the context of cost—specifically, the cost per gigabyte. That 300GB 320 Series drive runs $25 less than a 510 Series with 50 fewer gigabytes under the hood. To put things into perspective, let's look at each SSD's cost per gigabyte, which we've obtained using current Newegg prices and the amount of storage capacity accessible to users in Windows. A Western Digital Caviar Black 1TB mechanical hard drive has been included for reference, and the bars have been color-coded by drive family to make the results easier to follow.

Depending on the drive family, higher-capacity models can be slightly better values than their less capacious counterparts. The Force Series 3, m4, and 510 Series all cost less per gigabyte if you climb the capacity ladder. However, the reverse is true for the Force Series GT and the Intel 320 Series, which are better deals at 120GB than at 240GB and 300GB, respectively.

These cost-per-gigabyte calculations are sensitive to prices that change seemingly every few days at Newegg, so the results certainly aren't set in stone. However, the overall landscape has looked pretty consistent of late. The Crucial m4 and the asynchronous SandForce drives are among the cheapest 6Gbps drives around, while the 510 Series stubbornly resists discounting. Everything else tends to fall between those extremes.