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Comment: A Few Days or Essentially Forever (Score 5, Informative) 214

by arrianus (#19960163) Attached to: Sony's Solid State 2.4 Pound Laptop Reviewed
Flash media will typically have about 100,000 read/write cycles before failing. It's sometimes advertised as millions, but practically, no one makes media that goes over 300k, and no one makes media that goes under maybe 10k. Used naively (e.g. CompactFlash in an IDE-to-CF adapter as your / partition), the time to failure is on the order of days. Log files, file access times, and bits like that get written over and over and over, with some files being touched every few seconds. You've got 86,400 seconds in a day, which is in the same ballpark as flash endurance. I've seen drives fail this way.

Used properly, however, a SSD will last forever. Typically, the drive will include load spreading somewhere in the chain. The algorithms are a bit more clever than what I'm about to describe, but naively, if you've written the same location more than a few times, you move that data to a different location. This are often implemented in the drive's firmware, but may also be implemented in the file system (Linux comes with a few flash file systems that do this -- indeed, OLPC uses one of them). Used this way, the solid state drive will last for many decades of continuous use before failing, and will eventually fail for the same mechanisms as any other old IC. A 40GB drive, written at 100Mbps, will take about an hour to overwrite completely. With an endurance of 100,000 cycles, you get a bit over 10 years of continuous write at that speed before you run into endurance limits. With normal write frequencies, that means it'll last essentially forever.

Data is stored as charge on a conductor surrounded by insulator, but the insulator isn't perfect, and eventually, electrons do drift on and off. As a result, data stored in flash has a lifetime on the order of 10 years if it doesn't get refreshed. Of course, refreshing it is trivial (read out data, write it back).

Of course, with a Sony laptop, the major question isn't drive lifetime, but how long until the hinges or latches break. Sony laptops typically frequently have mechanical failures within a few months of purchase. Sony skims on quality quite a bit, these days, and is mostly running on reputation for quality acquired many years ago. That, combined with shooting for the lowest possible weight (and skimming on construction quality to save weight too) makes for pretty flimsy laptops.

IF I HAD A MINE SHAFT, I don't think I would just abandon it. There's got to be a better way. -- Jack Handley, The New Mexican, 1988.

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