[was: Cutting the power ... ] Journaling file system

[Warren Block]

On Mon, 19 Jan 2004, Cordula's Web wrote:

> Beware when using flash ram as some kind of live filesystem!
> Flash media has a quite limited number of erase cycles
> You may think that's plenty, but since filesystem meta-data
> is often written at the same location (superblocks etc...),
> this location will quickly reach the threshold, where it
> can't be used anymore!

Current flash memory spreads the writes around through "wear leveling."
A logical write to an address is remapped internally to keep the wear as
even as possible.  There's a kind of neat calculator at:

http://www.m-sys.com/content/Developer/Calc.asp

There's also a PDF from the same company that talks about how it works,
but I couldn't find it on their web site, so:

http://www.spezial.de/commercio/dateien/magazin/FFD_Life_Expectancy.pdf

-Warren Block * Rapid City, South Dakota USA