SSDs have controllers that count the number oftimes

Tag : hard drives
I doubt that there are many other people in the technical landscapewith enough sense of humor to equate the evolution of horses andcars to hard drives and solid state drives (SSDs), but here I am.Horses, for the most part, were reliable, low-cost, had predictableoperating parameters, and were cheap to operate (grass). Cars, onthe other hand, were noisy and smelly (neglecting that horses hadtheir own unique fragrance), had suspect reliability, had anextremely high purchase cost, had unpredictable operation (badroads), and fuel was hard to find (no gas stations). We should allstill be riding horses, right?
That would certainly be the case if this was strictly aprice/performance comparison of two nonevolving technologies at asingle point in history. But cars continued evolving while horsesdid not. Flash memory is a similar story of evolution. Embeddeddevelopers, iPod users, cell phone crazies, digital photographers,etc., all rely on the significant advantages of nonvolatile flashmemory as a core design element in the functions of these products.Of course, incorporating flash successfully had its learning curvesand some experiences are hard to forget.
Back in the early 1990s, I was called in as a consultant to help acompany having problems getting one of its new communicationproducts to stop failing. The device was unique for the time andoffered significant advantages over the competition. The bad newswas that after about two weeks of operation, it lost its marbles(i.e., forgot all its setup information and user inputs). I supposeI could have milked the job for a few days playing with a scopeprobe, but after looking at the schematic, I chuckled and asked thesoftware guys how often they were writing the setup information tothe flash memory.
You know software guys. When doing a task one time works, doing ita whole lot more often is better. ;-) It turns out that they wererefreshing the configuration and user settings to the on-boardflash chip every time they dumped the communication traffic RAMbuffer to the hard drive—about once a minute. Worse yet, theywere writing it to the same flash memory address every time. Iguess no one on the hardware team told the software guys that anysingle address on the flash memory was only good for about 10,000write cycles. It should have only lasted one week. They were luckyit lasted for two.
I can’t speak for all embedded engineers, but it isexperiences like these that add a certain personal skepticism aboutincorporating flash memory in everything. Certainly, technology haschanged a lot through the years and flash write cycles are now inthe hundreds of thousands (I believe I even heard 1 million quotedby one vendor) and flash makes absolute sense in digital cameras,cell phones, and A/V gadgets. The likelihood of writing to anysingle address a couple hundred thousand times in an 8-GB MP3player or camera memory is so remote that all skepticism isremoved. Flash cards in these devices just aren’t worked allthat hard.
Flash-based SSDs (versus spindle hard drives—HDDs) is anotherstory and still a work in progress. Like the horse-versus-carscenario, there’s no doubt in my mind that in the long runSSDs will win, and at least for laptops and subnotebooks, thetransition will be sooner than later. SSDs survive hostileenvironments better than mechanical systems—HDDs don’tlike extreme high or low temperatures. (Ever try starting yourlaptop after it’s been sitting in the trunk overnight duringthe winter?) Higher random access data transfer speeds overequivalent-size hard drives—still a lot of testing going onbut electrons beat mechanical rotation. Highreliability—beyond environmental attributes, SSDmanufacturers quote significant life spans in normal use. Moreenergy efficient than HDDs—this appears to depend on brandnames and the SSD generation technology.
Still, for a graybeard who knows that flash chips have write cyclelimitations, stuffing a $1,000 SSD in my next notebook so that allforms of Microsoft bloatware can disk cache the heck out of ituntil it turns into silicon dust is a hard sell. But, old dogs canlearn new tricks, and disk endurance is one of them. HDDs are good,but SSDs can ultimately be better.
Writing to flash in an SSD is not the same as writing to a rawflash chip. Specifically because they incorporate life-cyclelimited technology, SSDs have controllers that count the number oftimes that memory blocks are written to and dynamically reallocatephysical blocks transparently to spread data across the wholememory space. Basically, you’d have to write a file the sizeof the entire SSD for whatever thousands of write cycles to hit theendurance life of any one cell. The controller provides many layersof virtualization between the software and silicon.
Don’t get me wrong. HDDs still have a long life, and it maybe years before the curves cross. The lowest cost/MB, high memorydensity, large data caches, and decent energy efficiency continueto extend their design life. Still, the handwriting is on the wall,and I can see the future. At least for one old dog, my greatestfear in using SSDs has been addressed.