Solid-state drives go mainstream

Will SSDs replace conventional magnetic hard drives anytime soon?

Just about everyone has heard the hype surrounding solid-state drives, but only now are we starting to see SSDs get a foothold as a storage alternative for everyday use. The market is flooded with options, and the performance we've seen from several of the latest drives in our tests back up some of the claims that SSD supporters have made about the technology's advantages.

The PC World Test Center evaluated eight SSDs and found that performance diverged widely among them, as well as compared with magnetic hard-disk models. To see the test results for the top five SSDs, consult our solid-state drives chart.

Until the advent of SSD, standard PC storage relied on magnetic hard-disk technology, which has numerous moving parts (including a spindle motor, an actuator assembly, and read/write heads that float barely 10 nanometers above the spinning platter surface).

By contrast, SSD storage consists of NAND flash-memory chips. SSD's lack of moving parts gives it an edge over regular drives on multiple levels. First, SSDs are more shock-resistant than magnetic hard-disk drives; SSDs have fewer potential points of mechanical failure, and are able to withstand jostling and sudden impacts. Second, SSDs are silent, which makes them great for PCs that sit in living areas. They also generate less heat and use less energy, so they don't require fans, which contributes to their quiet operation as compared with a spinning hard-disk drive. Finally, because of their compactness, SSDs can be designed to fit in tight spaces.

That said, today's SSDs primarily adhere to the current 1.8-inch and 2.5-inch hard-disk sizes, and typically they use the same connectors as hard-disk drives do (first Parallel ATA, now Serial ATA-300). An SSD can easily fit into a current laptop or desktop chassis using existing industry standards. As a result, buyers should think of SSDs not as replacements for regular hard-disk drives but as complements to them.

In pricing, SSD currently has little hope of competing with standard hard drives, and this won't change anytime soon. Expect to pay upward of $4.50 per GB for an SSD, versus about 25c per GB for a regular hard drive. Capacity remains relatively limited, too: 256GB is the current high end for mainstream SSDs. (A few outliers, such as the OCZ Colossus, reach 500GB or even 1TB, but they have a stratospheric cost and come in a 3.5-inch chassis.) Because of that limitation, SSD makers don't target storage-hungry users. If you need high capacity, look to standard hard drives; they can offer more than triple the capacity of SSD at a fraction of the price. (Another possibility for desktop PC owners who want the best of both worlds: Use an SSD as the primary boot volume for your apps and operating system, and use a roomier regular hard drive to store data.)

Despite its disadvantages, SSD is breaking into the mainstream due to the proliferation of models and the lower prices that have come in the last year from increased competition and improved production processes. Notably, Intel recently introduced its smaller and less expensive 34nm NAND multilevel cell flash memory.

SSD Pros and Cons

Performance sees improvement, too, but the benefits of using an SSD are not apparent across all applications. For now, SSDs force you to accept a trade-off: They offer faster read speeds, but in write speeds they trail 7200-rpm magnetic hard disks (and can even fall short of 5400-rpm hard disks).

Compared with standard hard drives, SSDs are capable of reduced latency, which translates into greater speed in accessing data. For example, Intel says a typical hard-disk drive's latency is 4000 microseconds, while the company's X-25M is rated at 65 microseconds. SSDs have faster seek times than hard-disk drives do, too. Newer drives, such as the X-25M, boost random write performance, which can have a positive impact on system and app responsiveness.

But not all SSDs are created equal. Everything from the source of the NAND flash to the chipsets and controllers to the wear-leveling algorithms used (more on that in a moment) can affect performance. Single-level cell (SLC) flash, for instance, is costlier than multilevel cell (MLC) flash, but it's also capable of greater endurance. Most consumer SSDs today have MLC flash; when drives are significantly pricier or are sold as "enterprise" drives, the reason may be that they have SLC flash.

Although the SSD market is crowded with contenders, only a few companies, such as Intel and Samsung, manufacture the flash memory. They supply the flash — and often the drives themselves — to other vendors, which "rebadge" the drives as their own. For example, the Corsair model I reviewed for this story is a Samsung drive inside. (Even though we list a Samsung model in our SSD chart, the company does not sell its drive directly to consumers. Instead, it sells the drive to laptop makers and other drive vendors.) Next year I expect the market to thin out, with a few makers rising to the top, as SSDs aim for broader, mass appeal.

One largely unpublicized, but critical, aspect of SSDs slightly reduces the technology's attractiveness. In comparison with hard-disk platters, NAND flash memory cells can rapidly wear out with use. As a result, SSD makers employ wear-leveling algorithms to make the drive write data evenly across the flash cells. Whether the algorithms are effective in the long run remains to be seen, however. And consumers must accept a manufacturer's word as to how well its algorithm will safeguard their data; users have no way to gauge the drive's actual wear-leveling effectiveness.

Another little-discussed issue: Out of the box, SSDs can offer blazing speed, but over time their performance may degrade, depending on how you use the drive. Unlike with standard drives, with SSDs the sequential or random nature of the writes will affect future performance. Sequential writes generally leave a few large blocks of free space that make recycling, or garbage collection of data, faster. Every operating system, however, performs random writes that users can't control; in random writes, the remaining space is very small, and that causes garbage collection to take a lot of time.

Some manufacturers, Intel among them, estimate the lifetime of an SSD in its specs (Intel says five years). Along with other SSD makers, Intel also uses the same measurement that standard hard-disk drive manufacturers use, referring to the drive's life expectancy in terms of the mean time between failures. Among the SSD drives whose makers list this spec, the typical MTBF is between 1 million and 1.2 million hours, though at least one (Samsung) goes as high as 2 million hours, putting SSD at or above enterprise-class hard-disk drives in reliability, and far above consumer-class hard-disk models; manufacturers don't even list this spec for consumer hard-disk drives. (See "Hard-Drive Failures Surprisingly Frequent" for more about hard-drive vendors' MTBF claims.)

Hits and Misses

In our tests of eight drives, three eclipsed the rest of the field. (To see test results for the top five, check out our solid-state drives chart.) Leading the way was Intel's X25-M Solid State Drive 160GB. The newest Intel SSD drive bested last year's model, whipping through our tests and coming out ahead or in a statistical tie with our number two, the Samsung MLC SSD 256GB. A few seconds behind them was the Corsair P256--not a surprising result given that it has the Samsung drive inside.

In the middle were Patriot's Torqx 128GB and Super Talent's Ultra SATA SSD (also 128GB), decently priced at $525 and $480, respectively.

Bringing up the rear were two Ritek models (the RiData Ultra-S SATA 64GB and 128GB SSD) and Imation's 128GB M-Class Solid State. All three struggled in copying 3GB of files and folders, as well as in copying a single large file; they may not have been doing parallel writing, which can be necessary in a drive for dealing with the fact that flash's erase-write cycle is intrinsically slow.

Even though the Imation drive was slow, I liked two of its features: It sports a housing for use inside and outside a PC, and it includes a USB adapter for external use. You don't get that kind of long-term flexibility from the other drives here.

Given their still-high per-gigabyte price, SSDs have mixed appeal. The greatest value potential comes when you use an SSD in conjunction with an internal, standard hard drive (clearly, a less viable option for laptop users). SSDs are strong performers, especially on disk-read-intensive tasks, and an SSD can give an aging system new life; but before you grab one, you should consider whether the speed gains justify the sacrifice in storage space.

Tags solid-state drivesstorage

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Melissa J. Perenson

PC World (US online)

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