Linked by Thom Holwerda on Thu 27th Sep 2012 19:36 UTC
Apple I bought a brand new iMac on Tuesday. I'm pretty sure this will come as a surprise to some, so I figured I might as well offer some background information about this choice - maybe it'll help other people who are also pondering what to buy as their next computer.
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Alfman
Member since:
2011-01-28

christian,

"Do the maths. 3000 p/e cycles per block. So for a 128GB drive with ideal wear levelling, you can write ~3000 * 128GB. If you write 64GB a day (unlikely) you'd get 6000 days worth of writes. That's > 16 years."


I've got a few issues with your calculation. Obviously "ideal wear levelling" doesn't exist generically: what's ideal for one pattern is non-ideal for other patterns. And in fact a 128GB SSD is likely to be comprised of at least 8 NAND chips, which for performance reasons are running in parallel and may not take part in distributed wear leveling. So removing your assumptions might decrease your calculation by at least a factor of 8.

We are also talking about reliability on it's own, but in real devices reliability is one of many conflicting goals: performance, capacity, cost, dimensions. etc. The point I'm trying to make is that it's not safe to make assumptions. Even if the MTBF was 100% accurate, it only describes a curve with a multitude of failure points. Even with 3-5 years MTBF, you can still fail in a few months time. I'm just recommending those with write-heavy data loads take extra precaution against data loss with flash drives.

There was a study someone did correlating the jitter in flash performance to it's remaining data longevity. The older flash cells are, the more time it takes to re-program them. I'll try to find a link to it. It could offer a way of getting feedback about how much life is remaining on one's SSD.

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