[H-GEN] Idea for journalling filesystems

[Russell Stuart]

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On Mon, 2003-06-30 at 12:27, Jason Parker-Burlingham wrote:
> >> why not create it on one of those neato USB keychain drive thingies?
> > The only hassle I see is that there is a limit to how often flash may be
> > written to (it's getting better over time, but the limit is still there).
> 
> Bugger!  Do you have a source for this information?  It would indeed
> be a show-stopper for what's otherwise an excellent idea.  Trying to
> track down specs on these drives isn't exactly easy.  I'll take a poke
> at IBM's website, next.

The limit is actually the number of write / erase cycles.  Certainly if
you are always write the same area of flash over and over again it will
die quickly, but most flash file systems go out of their way to prevent
that.  Its called wear levelling, and it ensures that each flash cell
gets written to at a roughly equal number of times, even if you are
hitting the same byte in a file with each write.  It does come at a cost
- it typically doubles the number of writes done.

Your typical flash chip can withstand 100k write / erase cycles.  So
assuming your USB flash device is 32Mb, you will get to write that 32Mb
approx 50k times.  Ergo you will be able to write approx 1.5Tb to your
32Mb flash device before it fails.

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