Solid-State Drives Go Mainstream

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.)

Next: Hits and Misses

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