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The proper care and feeding of SSD storage

Jon L. Jacobi | May 14, 2013
Your solid-state drive sits there in silence. It's sleek. Elegant. More than a little mysterious.The hard drive it replaced was easy to understand: A soft hum assured you that its platters were spinning. A quiet mechanical click informed you of its read/write operations. You'd groom it with the occasional defrag. Times were good.

Your solid-state drive sits there in silence. It's sleek. Elegant. More than a little mysterious.The hard drive it replaced was easy to understand: A soft hum assured you that its platters were spinning. A quiet mechanical click informed you of its read/write operations. You'd groom it with the occasional defrag. Times were good.

Now? Everything seems peaceful. But you keep hearing stories: An SSD's performance deteriorates over time. They have disturbingly short life spans. If it fails, your precious data will be consigned to oblivion. Facts? Or fever-brained fiction?

A high-end SSD is the pinnacle of computer storage today. Ditching your hard drive for one of the latest SSD models is like dumping your go-kart and hopping into a Formula One car. I'm not exaggerating: SSDs can produce a four- or fivefold jump in speed. They have no mechanical parts to break, and they emit zero noise. SSDs are the perfect storage medium--until things go pear-shaped. Or until you seek hard information about the technologies involved.

A speedy drive with a few deep secrets
One reason you hear so much fuzzy information about SSDs is that the companies that design and build one of the key components--the memory controller--guard their technology secrets more carefully than Coca-Cola protects its soda formula. It's a very competitive and lucrative market, with just a few players.

And some of the facts that are available sound scary. Consider the read/write longevity of SLC (Single-Level Cell) and consumer-grade MLC (Multi-Level Cell) NAND memory, the storage media used to build SSDs: The former is typically rated to last 100,000 cycles, but the latter is rated for only 10,000. Relax--you'd need to write the entire capacity of the drive every day for 25 years or so to wear out all the cells. The latest TLC (Triple-Level Cell) NAND that Samsung is shipping is rated for only a few thousand writes, but you'd still need to write the entire drive's capacity for something less than ten years to use up the drive. No average user will ever come remotely close to that.

Life-prolonging techniques
Having the controller write to every NAND cell once before it writes to any cell a second time--a technology known as wear leveling--also helps to extend a drive's life span. Wear leveling ensures that no cell endures heavy use while another sits virgin next to it. Newer controllers also compress data on the fly before writing it to the disk. Less data equals less wear.

The final longevity booster is spare capacity, or over-provisioning. All NAND chips have more memory than their stated capacity--about 4 percent. This is used by the controller for operations, and to take the place of worn out and defective cells. If you've ever wondered why some SSDs come in rounded sizes such as 120GB and 240GB, when other SSDs and memory in general is sold in capacities that are powers of two (128-, 256-, 512GB, etc.), it's because many vendors set aside even more NAND to extend the drive's useful lifespan. For example, a 240GB drive is really a 256GB drive with 16GB set aside for over-provisioning.

 

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