On Thu, Mar 22, 2012 at 01:39, Jim Thompson <j...@netgate.com> wrote:
>
> Hmm, No, close, but not really correct.
>
> *all* flash will eventually fail if you write to it enough. It's physics.
I do not disagree of course. Fine with theory.
> SLC NAND flash is typically rated at about 100k cycles, while MLC NAND flash
> is typically rated at no more than 10k cycles. Via wear-leveling and
> over-provisioning ('spare blocks') you can increase these numbers, but no
> native flash device is rated in terms of millions of erase cycles.
You are talking about theory, the memory shell. I talk about the
actual flash disks.
There is a specific mechanism in these industrial flashes, doing
exactly this: When it finds an old memory shell refusing to be erased,
it re-allocates it ("on the fly" - transparently) to a healthy / not
used sector and marks it "bad", much like a hard disk. Read their
documentation.
Now, imagine an 2G or 8G flash disk, containing only 50 - 150 MBytes
of code, like PfSense or any other small "footprint" OS or
application. It will practically "never" stop working. Many many
millions of erase cycles.
In real life, not theory. For 20 or 40 $ price.
Of course, if you anticipate many writes like data logging or
something, there are special techniques to overcome it. Like using RAM
and compressing/storing to flash every hour or so. All "embedded"
flavor OSs are doing things like this.
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