Introducing Solid State Hard Disks (SSDs)

What you need to know to evaluate a Solid State Hard Disk

I'm writing this posting on a laptop computer that is, literally, in my lap. As I type, the poor machine gets bounced around which is not at all good for the hard disk. I'm tempting fate, perhaps the computer equivalent of driving without a seat belt.

I would be much better off if the computer had a Solid State Hard Disk (SSD) rather than the traditional hard disk with rotating platters. Hard disks are amazing feats of technology, but they are moving mechanical devices and nothing good comes from bouncing them around, be it on your lap or carrying a notebook computer around the room while it's running.

No doubt more and more laptop computers will move away from rotating platter, traditional, hard disks to Solid State Hard Disks because, in may ways, SSDs are better.

Because SSDs use flash ram to store data, there is no risk of mechanical failure. And, even though hard disks spin pretty fast, compared to the other internal components they are serious slow pokes. As a rule of thumb, SSDs are faster than traditional hard disks, but more on this below.

More power is needed to make hard disk platters rotate than is needed to power the flash ram in SSDs. Thus, laptop users can get more run-time from the same sized battery. Or, a computer with an SSD can be smaller and lighter because the same run-time can be had with a physically smaller battery.

Rotating hard disks generate heat, which needs to be dissipated. Without this heat, laptop computer designers may be able to omit the fan making the computer smaller and quieter. This was the case with the original Asus EEE laptop computer.

The big thing holding back adoption of SSDs is, of course, the price. Today, for example, if you want an Apple MacBook Air, opting for the SSD adds $999 to the price.

Much of this is common knowledge. A couple blog postings by Matt Kohut of Lenovo have a lot to add.

First Generation SSDs

In his first blog about SSDs (see Solid State Hard Disk Drives) last August, Kohut noted that things were changing drastically between first generation and second generation Solid State Hard Disks. Tests by Lenovo concluded that first generation SSDs didn't cut the mustard which is why, at the time, they didn't offer SSDs on any of their laptop computers. Kohut says that Lenovo was waiting for assorted improvements offered by second generation SSDs.

I was surprised to read that in their testing Lenovo found no power savings with first generation SSDs, compared to traditional hard disks. How could this be? According to Kohut first generation SSDs:

"... with a Serial ATA interface are actually Parallel ATA hard disk drives with a serial bridge chip. They don't offer support for low power interface states and the architecture has a potential for data-losing error conditions when recovering from a low power state like suspend or hibernate."

One of the features Lenovo was waiting for in second generation SSDs were true SATA interfaces.

Read/write performance offered another interesting point. While first generation SSDs were very fast on random reads and slow on writes, it's not that simple. Quoting:

"Performance numbers are inconsistent and very dependent on factors like percentage of space used and file fragmentation. Those benchmarks with sequential reads or writes will have markedly different results than those testing with random reads and writes. Internally, our team has benchmarked performance to be anywhere from 3X the performance of a hard drive to less than a standard hard drive. Proceed with caution when someone throws numbers at you."

As for shock resistance, Kohut reports that SSDs are six times more shock resistant than normal hard disks.

Blog Posting Part 2

Six months after his initial posting, Matt Kohut wrote Solid State Hard Disk Drives (SSDs) Part 2 (March 2008) This posting too, is a recommended read.

It seems that Lenovo was practicing Defensive Computing regarding Solid State Hard Disks:

"SSD technology is new. It is undergoing growing pains, and while Lenovo took a lot of heat from our customers for waiting so long to ship an SSD option, we did this for one primary reason. IT'S YOUR DATA and it requires a lot of care to keep it safe. Anything that replaces a tried and true technology for something new should be approached with skepticism until it has proven its worth in the marketplace and has been tested, retested and tested again."

Reporting again on tests by Lenovo engineers, Kohut says:

"Over the time our engineers have been evaluating SSDs, they have learned a lot about what makes a good drive vs. an average drive. All SSDs are not the same and anyone who is evaluating them should do extensive testing. Lenovo testing has shown that some drives from even name brand manufacturers are considerably slower than hard disk drives, especially when writing data. Others are significantly faster for random read operations. Even in a manufacturer's own line, there can be significant differences in performance."

He revisits the interface issue and notes that native SATA interfaces are on the market and he highly recommends them over older SSDs that packaged a parallel drive with a SATA bridge chip. As for power consumption, Kohut says that while all SSDs save on laptop battery life, their power consumption varies, with native SATA drives being the best.

The highlight of this posting, at least for me, is the comparison between the SSD in the Macbook Air and that in Lenovo's ThinkPad X300. The X300 uses a second generation SSD, the Samsung's RBX. Quoting:

"The MacBook Air uses Samsung's older N880X drive. While both are currently shipping 64GB-capacity Samsung drives, the NBX drive that Lenovo uses is 2X+ faster. It has had more growing pains (bugs) worked out of it. It uses SATA technology instead of older Parallel technology with a SATA bridge chip. Compare the ThinkPad X300 with the MacBook Air if you must, but at least give us credit for using a more advanced HDD technology."

Sure enough, the tech specs for the MacBook Air simply refer to a "64GB solid-state drive" and offer no further details. Finally, some ammunition for John Hodgeman. :-)

Ending on a Defensive Computing note, Kohut points out that the worst case scenario with SSDs is much worse than the worst case scenario with traditional hard disks. By worst case, I'm referring to a hardware failure of the disk drive that cuts you off from the only copy of important files.

With traditional hard disks, this may cost you a couple thousand dollars, but there is an excellent chance the data can be recovered. With SSDs however Kohut says "Today if an SSD drive fails, there is currently no commercially available way to get that data back. Anyone using an SSD drive MUST have backups."

I will have more to say about backing up your computer.

See a summary of all my Defensive Computing postings.

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About the author

    Michael Horowitz wrote his first computer program in 1973 and has been a computer nerd ever since. He spent more than 20 years working in an IBM mainframe (MVS) environment. He has worked in the research and development group of a large Wall Street financial company, and has been a technical writer for a mainframe software company.

    He teaches a large range of self-developed classes, the underlying theme being Defensive Computing. Michael is an independent computer consultant, working with small businesses and the self-employed. He can be heard weekly on The Personal Computer Show on WBAI.

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