MTD_PHRAM - what filesystem to use?

[Jörn Engel]

On Sun, 11 March 2007 22:08:35 +0100, Sam Ravnborg wrote:
> > 
> > Write rate is 10kB / 10s * 1.1 = 1.1kB/s.
> > Total written data in 10a is: 1.1kB/s * 31536000s/a * 10a = 346GB
> > Required flash size: 346GB / 100k = 3468kB
> 
> I assume that from a performance point-of-view the FLASH based version
> suffer more than the RAM one - since it is simple to 'erase' RAM.

Not likely.  With the example numbers, 1.1kB/s will be peanuts compared
to flash write bandwidth.  Erases happen ahead-of-time in JFFS2, so
those won't matter much either.  Reads won't matter at all, if you are
looking at 100kB or so - all of that can easily be cached.

If you require a significantly higher write bandwidth, the required
flash size will equally increase.  Who knows, battery backed RAM may be
cheaper than flash due to the required size before the bandwidth becomes
a problem.

Good luck with your design, Sam!

Jörn

-- 
If you're willing to restrict the flexibility of your approach,
you can almost always do something better.
-- John Carmack