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The proper care and feeding of SSD storage

Treat a solid-state drive like its mechanical cousin and you could end up in a world of pain. Here's how to handle these exotic beasts.

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.

Higher capacity can mean better performance

With hard drives, the faster the spindle speed, the faster the drive. The amount of cache also comes into play, but by and large, a 10,000-rpm drive is faster than a 7200-rpm drive, which is in turn faster than 5400-rpm and 4800-rpm drives. That's an easy and intuitive metric for comparison shopping.

There is no spindle in an SSD, but there is a comparative metric directly related to capacity. Up to around the 256GB level, PCWorld's testing has shown that a larger drive will be faster than a smaller drive, with other factors (such as the controller and the type of NAND) being equal. To understand why, you need to understand how data is written to SSDs.

With a hard drive, data is basically written serially, down a single channel. The stream may be interrupted by existing data, but ideally it's all written in a neat, uninterrupted line. Inside an SSD, data is written in a scattershot, parallel fashion down multiple channels to the multiple NAND chips at once. The more NAND chips an SSD has, the more channels it has to write/read across, and the faster the drive will be.

You can find a perfect example in Intel's latest 525 mSATA (Mini-SATA) drives. Read the specs, and you'll see that the 30GB model is rated for 7000 4k operations (read-write operations) per second and 200 MBps sustained reading, while the 240GB version is rated at 46,000 4k operations and 550 MBps, even though both drives use the same 25nm NAND and identical SandForce controllers.

SSD optimization is unnecessary

Until recently, the common SATA 3-gbps interface was fine for any type of storage. A modern SATA 6-gbps SSD is backward-compatible with that standard, but it requires a SATA 6-gbps interface to realize its full performance potential. Soon enough, even that standard won't be fast enough, as the fastest SSDs we've tested can already write at speeds nearing 5 gbps.

Common wisdom indicates that there's really no way to optimize an SSD using a software utility. When you think of the manner in which data is written--scattered all over the drive--and the lack of a read/write head that you must worry about positioning, it's clear that the optimization techniques developed for mechanical hard drives don't apply to SSDs. In fact, the way an SSD presents data to your computer's operating system bears zero resemblance to how it's stored on the drive. Wasting precious write cycles trying to optimize an SSD is counterproductive.

How TRIM prevents performance degradation

There was a time when an SSD's performance would slowly degrade. That's because writing data to a previously used NAND cell is a two-step process: The cell must be erased before it can be rewritten. To increase write performance, an SSD controller would simply mark a used cell as no longer active and write data only to cells that had never been used. Once all the cells were used a single time, the drive's write performance would deteriorate because its controller had to erase cells before it could write to them again.

Nowadays, we have the TRIM command (it's not an acronym, despite the capital letters). TRIM is an operating-system order that instructs the SSD's controller to preemptively erase used cells containing unneeded data. TRIM is supported in Windows 7 and later, and it ensures that your SSD's performance will remain at its peak over time.

Recovering data from a failed SSD

SSDs, and solid-state storage in general, have a disturbing tendency toward binary functionality. An SSD failure typically goes like this: One minute it's working, the next second it's bricked. The latest drives are supposed to alert you when they're nearing the end of their useful life span, but what happens if the warning pops up and you're not there to see it? The solution, of course, is to back up your SSD in advance.

Contrary to common belief, however, data can be recovered from a failed SSD. DriveSavers, a California firm known for recovering data from hard drives that have experienced the most catastrophic failures, can perform the same service on SSDs. Whether the failure lies with the controller or the NAND itself, the company has a good, though not perfect, success rate.

That 'dead' drive may just be awaiting rescue

How is this possible? Many times, what seems like a hardware failure is actually a firmware failure. The controller simply encounters a situation it can't deal with, and locks up. If the controller is bad, you can replace it--provided that you can find the exact, correct model. Remember when I said that only a few companies are building memory controllers for SSDs? Well, some SSD manufacturers use what might look like an off-the-shelf controller when it's actually one built to their own specifications.

De-soldering chips is a painstaking task. I know--I've done it myself. DriveSavers has a robot for that work, or it would never be able to operate cost-effectively. The company has also developed proprietary recovery software that can re-create data from just the NAND itself, even if a bad chip is involved. Company reps were understandably vague when I asked about DriveSavers' techniques, but the bottom line is that you might be able to recover data from a failed SSD.

Some final SSD tips

SSDs are wonderful storage devices, but they're not perfect and they're not all equal. A no-name bargain unit might not be as good of a deal as you think because it probably uses slow NAND and an outdated controller. Shop carefully. Here are some additional tips:

  • Buy the highest capacity you can afford. You'll get better performance, although the benefit declines rapidly beyond 256GB.
  • If you're running an OS that doesn't have native TRIM support, check the manufacturer's website for a driver that will force garbage collection. You might also look for a utility that you can run occasionally to perform the same task.
  • Use your SSD for the computer's operating system and application software. Store your movies and most of your other data on a mechanical hard drive. Hard drives stream media just fine, and they're often better suited for simultaneous recording and playback. They're also at least ten times cheaper per gigabyte.

SSDs may seem exotic and mysterious, and they're still pretty expensive. But they have significant performance advantages over traditional mechanical hard drives. Now that you know their secrets, you can shop smarter for these sleek storage devices and take the best care of the one you bring home.


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